Project 68mm – Pt4

Well here we go again, the new RE274 cam installed. The cam itself is 274 Duration on the inlet and 270 on the exhaust, but it may come out a few degrees more with the 1.5 Ratio rockers. My Re13 cam is 276 duration on the inlet and 236 @ .050″ The 274 cam is 274 duration and 248 @ .050″ The exhaust lobe is 270 Duration and it is 244 @ .050. This grind really needs to be ground on a wide lobe cam (1275 type). So you can see that it is a couple of degrees smaller @ Advertised duration but it is a lot bigger from .050″ onwards, So you get the advantage of a smaller duration cam, but bigger duration once you get it open to fill the cylinder. So in theory we should get the advantage of a small cam for low down torque, but the bigger duration once the valve is open. So it is going to help carry the torque further through the RPM and should make more power in the mid to upper RPM range.
As we saw the last time the big head lost horse power and torque through the range as the head was just a little too big for the RE266SS cam. So hopefully the RE274 cam will bring the head to life.


Click image to enlarge

After running the cam in we gave the string a pull and things looked very promising, a little fiddle with the timing saw it use a couple of degrees more advance.Then back to the carbie, I went up one jet bigger in the main, I didn’t loose a thing down low but it improved the top end. As you can see by the dyno sheet the little motor made really good horsepower, but I had been hoping to make around 125HP and at least a solid 100ft/lb of torque. But it wasn’t to be.


Click image to enlarge


Click image to enlarge

The down side to this cam is that we lost all the low down bottom end. Where the RE266SS would take full throttle at 1500RPM with the smaller head, The RE274 cam and bigger head I was struggling to get a solid reading down at 3500RPM. This doesn’t mean that it won’t pull away from 2000 RPM at part throttle though.
So if you are going to build a small bore motor (the little ones are great fun) Think about what you are going to use it for and what RPM you are to work in. Have a look at what we have done to achieve the results with this motor. With the RE274, it is going to be a little lumpy in the small bore motor, but if you want a lively cam that has to be driven hard and gives good midrange to top end, then this could be the cam for you.
This cam in a big bore would be a lot tamer. As you go up in capacity, it will make the cam a lot smoother. Another alternative would be to grind the exhaust lobe 270 duration on both inlet and exhaust. This gives you something in between the RE13 and the RE274.
Which ever way you go you are going to have a lot of fun with these little motors, and they will be more than capable of keeping up with the traffic.
One other thing that happened while dynoing, while testing the RE274 cam, the motor started to get a little miss, mainly in the higher RPM. After trying the plugs, points and jetting it was time to change the head gasket and have a look at the head. The gasket looked ok, so lets look at the ports. No sign of water getting in the chambers, all looked ok, just carboned up. All the same colour, so a new head gasket and try it again. The miss was still there, turn off the motor, scratch head, give it a rev to 8000RPM and see what happens.The miss was alot worse. Time to check the tappets. Taking the rocker cover off, it was very milky, try to turn the motor over, locked solid…. Pulled no.1 spark plug out and out comes water! Not Happy! So the water was drained out of the motor, crank the motor over with no plugs to get rid of the water. Plugs back in and a quick rev to 6000RPM on full load, no miss. It had cleared all the water out of the cylinder. The motor was taken off the dyno for a customer motor.
Aaron the internet lemming, comes around the next day and pulls the head off and on very close inspection, right in the corner of the combustion camber, a tiny little hole was found. It was getting bigger the more it was run. This is the problem with 50 year old cylinder heads, they rust through from the inside out and we wind up being in this situation.


Click image to enlarge

So without the water leak, we could have seen more torque and horsepower if we had kept playing around. So we will try and fix the head and have another go. I also have another cam to try, it will be TOO BIG for the road, but I like to play with new cam designs. I still have a lot to learn about cams and designing new profiles. Just gotta keep playing.
We will be back after time for another cuppa and a bikkie.

Pt5, I think we will try going back to the 266SS cam and the 998 head that we modified in this article. Stay Tuned….

2014 All Mini Race – Morgan Park

Here is a spit screen video of my in car along with Santino’s at Morgan Park in 2014, where we raced in the All Mini event.


2015 Phillip Island Classic Group N

Another In car of Graham racing at the 2015 Phillip Island Classic

Little bit wet, a little bit more fun.


Muscle Car Masters 2014 – Racing with Andrew Bergan in the wet

Here’s a video of Andrew Bergan from Mini and Moke World have a ball racing in the wet. Slippery and Fun!

Thanks to Andrew for the Video from his car. Make sure you go check his website over at

Project 68mm – Part 3

OK, it’s time to get the motor back on the dyno with a few new bits and see how it stacks up.
With a new modified head, again based on a 12G202 head, it has inlet valves of 1.3″ in diameter, with a nice radius seat, all blended into the throat area and modified around the divider. The inlet port has been opened up a little more than the last head, but still not as big as a 12G295 head, yet. The head is flowing around 113 CFM at 25″ on my flow bench.

Flow benches are essentially a vacuum cleaner that can tell you the air flow rate. They tell big lies, heads are just like a drain pipe, the bigger the hole the more they flow. Yes, we need flow to make Torque and Horsepower, but it is the way we achieve the flow that really matters. We need velocity to fill the cylinder, especially at higher speeds. Just think about it, the valves opens and you have to get air moving from being stopped and it does not have a lot of time get in and fill the cylinder before the valve closes again. Now it takes a lot longer to get air moving in a big hole as it does in a small one. But you can go too a small with a port and the air becomes supersonic and stalls. This is not really the problem with a siamese inlet ports. You can defiantly go too big with a mini port, especially with road cars where you need to chase torque.

Now I’m not against big valves in a road cars as long as you keep the choke area down. One thing you must keep in mind, is the air does not flow through the diameter of the valve, but around the circumference of the valve. So with the bigger valves you have more area to pull from, but with the smaller choke area you will get the higher air speed across the seat to help fill the cylinder.

I’ll give you an example of what I mean. In my dyno room, I have a fan for pushing air in the room, now if I open the door wide open you can not feel the air exiting the room, but if you open the door about a third, you can feel the air rushing out. Now have a think about what I just said. This leads us to the curtain area of the valve, which is the amount the valve has to lift to equal the area of the valve diameter, which is about 25% of the valve diameter, no matter what the size the valve is.

The theory is that you don’t need to go any higher in lift than this, but of course, sometimes the theory doesn’t always work out and that is why we lift the valve 30-36% of the valve diameter. This is why I like camshafts with a large nose radius as you open the valve quickly and hold it open for as long as possible to take advantage of the high speed air coming in.

Now with this motor, I have my new 266SS camshaft fitted, which has 0.270″ lift on the lobe, minus the tappet seating which gives us 31% of the valve diameter in lift with the 1.26″ diameter inlet valve and 30% with the 1.3″ inlet valve.

Lets take a look at the exhaust valve and port. The valve I am going to use is 1.070″ in diameter. With the std exhaust valve which is 1″ in diameter, you can actually get quite a lot of air through this, but I like to a little bigger so I can get a better shape seat. So the first step is to cut the new seat, to get a nice radius and a good lead into the 45 degree seat. With the seat cut, lets put it on the flow bench.

1st Setup                                                      2nd Setup
Std Exhaust port and Std Bowl                Modified bowl and port

Lift              Scale                 %                Lift                Scale             %

0.50             110                    50               0.50             110                 52
0.100                                     63               0.100                                  65
0.150                                     71               0.150                                   74.5
0.200           150                   58               0.200          150                  61
0.250                                     60.5            0.250                                  69
0.300                                     62.5            0.300                                  66
0.350                                     62.5            0.350                                   67
0.400                                     63               0.400                                  68.5
0.450                                      64.5           0.450                                   70

Next we tidy up the bowl and remove the guide boss.
After doing this test, I then decided to open up the exhaust port itself along with some reshaping, but not going too much bigger, I threw it back on the flow bench only to find out it makes no difference at all to the flow figures. The only thing I managed to achieve was to get the air flowing out of the port more smoothly, yet there was still no gain in flow. This means, a good clean up would suffice on STD head with this size valve, the exhaust port only needs to be around the same area as the valve. A big exhaust port is around 110% of the exhaust valve. We still need to keep high velocity in the port, so don’t go too big!

68mm big head68mm big head dyno

Well that was interesting, the motor did not like the bigger head, so when building a motor, you have to consider what you are going to use it for. If you are going to build a good road motor, don’t go overboard with cam and head modifications, as you can see by the dyno results, with the smaller cam you don’t need a big head to get good results.

What this head did do, was carry the power through to 8000RPM, which surprised me, as normally a cam of this duration would not carry that kind of horsepower through to 8000RPM. As you go up in cam duration, you are going to move the torque curve further up the rpm range. So think about what sort of RPM range you will be working in. This is why I am trying to design a new cam that can make strong torque and horsepower as low as possible in the rev range.

In the next article, I’ll be trying another cam(The new RE274) with this bigger head, to see if we can make it work.

Stay tuned for the next article.

Cuppa tea time now.

Project 68mm – Part 2

Well I finally got to get this thing on the dyno in it first iteration. Running the 44mm IDF Downdraft weber. See Part 1 Putting on some yellow paint marks on the push rods just to see how they should rotate, and all was well. See Cam Follower article  After running it in, I pulled the head down, re-set the tappets and we were ready to go.

With the tappets, I set them at 0.012″, but with the new 266ss cam, you can set them at 0.015″ if you would like to chase a little more torque. I will try this later and note the difference.

So lets pull the string, and the results were very impressive after a fettle with the weber and setting the timing. The timing was very impressive, it only needed 25 degrees total timing which means the motor is very efficient and means the combustion chamber shape, squish and swirl must all be working well together. One thing that was very impressive was the fact that is would take full load down at 1500 RPM, showing 57 ft/lb of torque. I have never had a motor on the dyno that would go down that low on full load!

Project 68mm dynoproject 68mm graph

For the next test, I took the head off and opened up the inlet port a little bit. I widened the port by about 1mm and squared it up a little. This port is not anywhere near as big as a 12G295 or 206 inlet port, but the results were a little bit better. What was very interesting was the torque @ 4500 RPM was 100 ft/lb. No matter how many times I pulled the string it still came up with the same result. What it did show was that we did not loose any torque down low and in the mid ranges, but as we got into the higher RPM the HP started to go up Where the STD port started to fall off at 7000RPM, the slightly bigger port held onto 7500 RPM.

Project 68mm mod inlet dynoProject 68mm mod inlet graph

The next setup to try was the 1 3/4″ SU on a Mini Spares Manifold, which was used with the same modified inlet port. What I did notice was that the SU was a lot smoother and gave a smoother spread of torque.

Two things cam out of this.
1. – The weber may work better with smaller chokes, say 33mm or 34mm instead of the 36mm that it comes with.

2. – The SU would defiantly work better with a longer manifold and may well go close to matching the weber.
The weber manifold is around 7″ long, So I will have to try the my long SU manifold which is around 7″ long.

The needle that I found to work best was a BBC needle.

Project 68 SU dynoProject 68 SU graph

With the original head working very well, I am not keen on modifying it too much, in case it ruins it. So the next thing I am going to try is a much more modified cylinder head. It has a slightly larger inlet valve @ 1.3″, but I still retained the 1.07″ exhaust valves and for good reason. When playing on the flow bench with the exhaust valve and port, it was very interesting. I will show the results in a later article.

Check back soon for Part 3.


Project 68mm – Part 1


Before reading this, I suggest the reader go back and read Project Small Bore Pt1, Pt2, Pt3 as lot of things in that project are relevant to this project.

The beginning of the process of building the 68mm project motor starts with boring the block. Looking at the block from cylinders 1 to 4 (right to left) or water pump to oil pump, the block needs to be offset bored

no1 cylinder needs to be offset towards the water pump by 0.025″

no2 cylinder needs to be offset towards the water pump by 0.025″

no3 cylinder needs to be offset towards the oil pump by 0.025″

no4 cylinder needs to be offset towards the oil pump by 0.015″

The reason for the no4 cylinder having a smaller offset is that you can run the risk of breaking through to the oil way at that end of the block. If this happens, it can be fixed by sleeving the oil way.

Once the block is bored, before honing, chamfer the bottom of the bores as the pistons will come out the bottoms of the bores at BDC and the bottom of bores, if not chamfered, become razor sharp and can shave the bottom of the piston skirt away.

When boring a motor this size, it is necessary to use a 1275 head gasket. Some people have put these straight on without any modification to the block and head. But the head gasket firing ring only just covers the water holes at the back of the block and could leak water into the cylinders. IMG_0005On cylinders one and four of the manifold side of the block, these have to be plugged and redrilled to match the head gasket. On the spark plug side of the block, cylinder four needs to be blocked off, but not redrilled.  IMG_0007
Another modification I like to make to the block is modifying the oil way behind the oil pump. This helps take the load off the pump and gives much better oil flow through to the block. I also do the one from the oil filter into the block.

IMG_0001 IMG_0002

This is not something you have to do, but every little thing helps. Once this is all done, honing can be completed and the block cleaned and prepared for mock up.

Main Bearing Bolts

In both the small and the 1275 motors, but not the Cooper “S” motors, they used two types of main bearing bolts. One is just like any other type of bolt, but the other is quite special. If you have a look under the head of the bolts, one has a washer face like most bolts, but the other one is quite different. Under the head of the castleated one, you will notice that it is undercut where the shank meets the head. There is a reason for this, when you tension the bolt down, it pulls down on the outer edge of the bolt. You may ask so what? Now if you use the STD bolt, have a look at how it pulls down on the bearing cap, you will notice that it does not have very much bearing area because of the small washer face and the hole in the cap being a clearance hole. It tends to break the edge of the bearing cap away and looses tension. This however can be overcome by using an ARP 7/16″ high tensile washers under the head of the bolt. I have seen these STD bolts used in quick road motors and have gotten away with it. I don’t like doing this, for the sake of a few washers you can make it right. However, by using the castleated bolts, you don’t have this problem.IMG_0022IMG_0023


The crankshaft has been wedged and balanced as this helps with the harmonics of the motor.

image3 image4 image6 image7

One thing that does help 1100cc cranks is to have all the radii shot peened. This helps to prevent cracking around the radius of the pins and mains.


Con Rods

The con rods have been checked for straightness and bore size


This is the jig for straightening rods. It is very simple and not hard to make, but it is very accurate. From the centre of the rod to where the dial indicator is, is about 3″. At this point, it magnifies the bend in the rod, so you can get the rod straightened very accurately.

I have also machined .150″ from the sides of the rods and balanced them, just to get rid of a little weight. My preference is to use 3/8″ high tensile cap screws or ARP bolts, rather than cheap bolts made from rubbish steel.



The camshaft I am starting with is the new 266 that I have designed. It has .266 duration. The duration can be altered by different tappet settings, because of the opening ramp I have used, you can set the tappets from .012 – .015″ which effect the seat duration of the cam.
The lift is 0.270″ on both inlet and exhaust, But I am running more duration on the exhaust than the inlet. The rate of acceleration is a lot greater that your normal 266 type grinds.

Another cam we shall try is my new 274 grind, which has .274 duration on the inlet and .270 on the exhaust. It has 0.312″ lift on both inlet and exhaust and also has a faster acceleration. This one may need some good springs to make it work well.

When a new cam goes in, it is important to use new cam followers or have the old ones reground. When I fit a new cam, I always regrind my followers weather they are new or old as a lot of followers do no have the correct radius. (See cam followers) The radius on the followers can vary from 34in radius up to 76in radius. A lot of followers today have very little radius and some are just completely flat.


Now that we have all the components for the short motor, assembly can be completed.

Cylinder Head 

The first head I am going to use is an 12G202 head with 1.260″ inlet and 1.070″ exhaust.

As per the block, the water holes in the head need to be modified to suit the 1275 head gasket.

On the manifold side of the head, the number one and four holes at the ends of the head need to be blocked and redrilled to suit. Whilst on the sparkplug side, the number one and four will need to be blocked off and not redrilled.




The choke area I am using under the valve is very small at 80% of the valve size. I am trying to get more torque into the little motor. The exhaust has an unleaded insert fitted in it. It’s running a full radius seat with a big top cut. In regards to the chamber, don’t try to relieve the exhaust valve to much as a slightly smaller area around the exhaust valve will help funnel the exhaust gas towards the valve, rather than have the gas running around the chamber trying to find a way out.


The chambers have been modified to suite the valves and to reduce compression as flat top pistons have been used. What I am going to do is use a STD inlet port and a STD exhaust port, then take some readings on the dyno. I’ll then take the head off and modify the inlet ports and redyno. This will give us an idea of what modifications make to the performance of the engine.

To fit the exhaust seats I use a purpose made cuter to cut the head. The insert is generally 0.005″ to 0.007″ bigger than the hole in the head, depending on the seat or the type of head being used. I use a Sunnen seat machine to cut all my seats and fitting inserts. There is a range of hardness in the inserts with the hardest of all being the ones used in LPG powered cars. They wear extremely well, but can be very hard on carbide cutters when cutting  the seats.


The rockers we are going to test with are the OLD type Keith Dodd 1.5s

Now that some of these rockers are getting older and some may need to be refaced. Not a lot of people have the jig to regrind them anymore, but they are still around. When I bought my valve cutting machine, it was optioned with this extra feature, so I bought it. This machine was the first one they had ever sold with this option, as not many cars use rockers as used in older cars like the mini do.IMG_0025

On thing to make sure of is the setting up of the rockers. When rebuilding a STD motor or building a performance motor, you deck the block, face the head, grind the cam and cam followers. They all affect the angle the rockers work across the tip of the valve. If it is not setup up correctly to work at the correct angle, you will be wearing out valve guides very quickly. So lets look at setting them up correctly. If you have a valve lift of lets say 0.400″, at half lift 0.200″, the centre of the pad would be in the centre of the valve. To achieve this, you may have to pack the rockers up or maybe machine down the bottom of the posts.

Now the head and rockers are ready, they can be added to the short motor to complete the long motor. The long motor was added to a gearbox and clutch housing ready to run on the dyno.



The extractors I am going to use on this motor are the maniflow medium bore as people can relate to these extractors and are easy to get hold of, and a lot cheaper than mine….


The Carburettors that will be run on the motor will be a single 1 3/4″ SU on a Mini Spares manifold. The other will be new toy, a 44mm IDF downdraft weber on my new manifold.



The dissy used will be a STD 29d with vacuum advance.


The long motor was set to a gearbox and clutch housing and readied for the dyno.

photo 2

Again, the reader should go back and read the Small Bore Project articles, as they will go into more detail as to what else was done through this build.

In the next article, we will run it up on the dyno, in it first configuration to see where this setup is at.

See Part 2 here


Camshaft Followers

Cam Followers
There has been alot of talk abut cam followers in the mini (A-series) community of late. So I thought it would be a good idea to go through and explain a few things.
When you assemble a motor and wind over by hand the push rods should rotate at least a quarter of a turn per revolution. Some followers maybe a little tight in the block, they should be able to fall in with there own weight with light oil.
Here’s a video that shows the rotation of the pushrods with correctly ground followers.
Most followers today in a mini should have a radius of around 72-74” to get them to rotate correctly. 95% + of the followers I’ve been getting lately have been all but flat, with virtually no radius at all. To check the radius on the followers, it is very simple. Place the followers of a sheet of glass or a flat surface, tilt the follower to one side and you should be able to get 0.0025 to 0.003 feeler gauge under the high side of the followers. If you can’t, I suggest you get them reground.
Here are some photos of some brand new followers that I have just touched to show the problem.
 The follower in the top left, shows how a follower should look when correctly ground. The rest have been just touched to show the incorrect way they had been ground.

Click to picture to enlarge

Cam follower quality issue continues…..Despite shouting from the roof tops for months on end now about major issues with A-series followers being supplied from the vast majority of A-series specialists and cam manufacturers, many are either sticking their heads in the sand hoping the problem will go away or simply not believing there is an issue. These pictures will hopefully underline the seriousness of the problem. Checked before fitting showed the followers to have flat faces, not the std. radius profile required for proper rotation.
IMG_0007Click to picture to enlarge
A Kent MD266 cam and follower kit was purchased, built in to an engine which I then ran on my dyno for a few hours. Paint dabs on the push rods showed the followers were not rotating. The motor was stripped down and followers removed for inspection. As can clearly be seen by the wear stripe across the faces, the followers were simply going up and down, not rotating (two wear rotating fully, and two were oscillating back and forth, while four were just not moving at all). Further proven by the wear on the sides of the followers. The wear line should be all he way around the follower sides, top and bottom. The wear fore and aft on these followers line up with the stripe across their faces. These followers would have wiped the cam out in a couple of hundred miles. IMG_0002

Click to picture to enlarge

Manifold with a difference


Here’s a new manifold I have been playing with, using an IDF Downdraft Weber. In a back to back comparison with a 45mm Sidedraft Weber and a fully ported short Redline manifold, it was 5-7Ft/lb of torque better across the board from 3-6500RPM.


The 45mm wouldn’t take full throttle below 3500 revs. Where as the downdraft would go down to 2500 revs. The beauty of this setup is you don’t have fuel blowing back in your face through the speedo hole, and hopefully doing away with the fuel smells you get with the sidedrafts. And yes, it does clear the bonnet and you can get a thin air filter on it too… Just.


This will be one of the manifolds that will be used on the new small bore project motor on the dyno. Keep checking back!

Manifolds Manifolds Manifolds

photo 2

The RE5 Weber Manifold is in stock and ready for sale.

I know sometimes it takes time for us to get various products either in stock or machined up for sale. So having that in mind, Russell Engineering is working to have more products ready for sale without delay. This is good, as it means more time for a culpa and a bikkie.

photo 1

The RE5 Webber manifold is actually a 5.5″ Inlet Manifold designed to use with a 45mm weber. It can be used for a 40mm as well, but best with a 45mm. The inlet manifold is an easy way to gain a few HP for the A-Series. You can have a bit of a read over the small bore articles to get a better understanding on how and why.

As you can see, we have plenty in stock and ready to go. So Contact us to grab yourself one. Of course you can also ask us about all our other products as well.

photo 3

July 2014 – Update

I’m sure you are all wondering what is happening with Project small bore Pt 4 and beyond, but like I always say, you can’t rush these things.

photo 2

In the mean time, a bit of an update as to what is happening here at Russell Engineering HQ.



1275 – 40″ and 60″ Pistons are back in stock. Along with all the other sizes that you may need. So if your are after some Contact me


We have also recieved a new shipment of manifold stock, for both SU and Weber. These are heat treated and ready to be machined to your spec. Once again, Give me a call to discuss

Inlet Manifolds
5″ Weber Manifold

SU HIF44/HS6 Manifold


POWER!!! or the lack of it

Last saturday saw some incredible winds throughout Sydney. These winds hit in the afternoon at REHQ. Having just completed a dyno run on Darren Burns’ motor for his Nb mini for the hit out at Morgan Park in Qld next weekend, a cup of tea was in order. However, the wind saw to taking out a tree near the front of the street, which in turn took out the power to the work shop. Havoc reigned at this point as the power runs across the street to the workshop. North Rocks Road is a busy road at the best of times and power lines down across the road is never a good thing. We managed to call the police and prop the lines up enough to keep the traffic flowing. All was well until a blind truck driver took out the lines without so much as stopping.

Long story short, power has only resumed on Wednesday, so if you were awaiting something, please be more patient than you already are.

photo 1


Project Small Bore

Its coming along and there are a bunch of new products being tried and tested. The project motor is heading to the dyno when time permits and the words and pictures are all but written on the build up to the dyno. So, please be patient as we work our way through bringing these new ideas to fruition. It’s going to be fun. I like small bore motors!

photo 3

Now, it’s cuppa time.

Graham Russell

Retro Speedfest 2014 – Sydney Motorsport Park

Project Small Bore Pt3

In the last article we chose a manifold based on flow volumes, and a carbie based on personal choice, but which combination is best on this engine?

With the engine finished, it is time to look at a variety of carburettors, inlet manifolds and exhaust extractors, to find the most suitable combination. There are a lot of figures, but they are necessary, so bare with me. But, before we do, we need to make sure the valve timing is set up properly. As I said in the last issue, even a very small difference can have a significant effect on the torque across the rev range. I also mentioned the standard Cooper S rockers have a tendency to be quite a bit inconsistent. This was perfectly illustrated when I came to put the rockers on this engine – boy what a mess! After changing the rockers around, I was able to get the four inlets somewhere near each other.

Table 1


Tappet                                   BTDC              ABDC                Duration               Lift

Inlet No 1 @ 0.016”              20                     60                        262                   0.332”
Inlet No 2 @ 0.016”              22                     56                        258                   0.328”

Inlet No 2 @ 0.014”              23                     59                        262                   0.330”
Inlet No 3 @ 0.016”              23                     60                        263                   0.332”

Inlet No 4 @ 0.016”              22                     61                         263                   0.332”
Exst No 1 @ 0.016”               55                     34                         264                   0.330”

Exst No 2 @ 0.016”               59                     40                        279                   0.345”
Exst No 2 @ 0.025”               52                     32                        264                   0.333”

Exst No 3 @ 0.016”                58                    38                        276                    0.340”
Exst No 3 @ 0.023”                53                    31                        264                    0.332”

Exst No 4 @ 0.016”                56                    37                        273                     0.336”
Exst No 4 @ 0.021”                51                    32                        263                     0.329”

As you will see from Table 1, all the inlet valve timings are pretty close to each other, at a setting of 0.016”. Only the inlet on No 2 cylinder needed adjusting, to 0.014”. But, the exhaust timings were still all over the place. This shows why some standard Cooper S were very quick, and some were only ‘not bad’. I decided to aim for a duration of around 263 at 0.016”, with 0.332” lift. To achieve this I had to adjust the rockers for the exhaust valves to some fairly radical settings. When they are this far out, you would be advised to look around for some better rockers. But, I decided to carry on with these ones to prove the point, that when they are adjusted properly they start to come back to where they should be. This motor has one of my RE13 cams in it, which should give a duration of 276 @ 0.016”, off the lobe, and a lift of 0.290” on the lobe. Because of the poor rocker ratios we were a little bit short on both duration and lift, but we will have to make do with what we’ve got. I have found that with setting up the cam on the small bore engines, they like to run slightly retarded – not split overlap or advanced. So, retard the cam 3 to 4 and you will get a bit more torque and horsepower. For this sort of testing, you’ve got to make sure all other variables are standardised.

I ran all these tests with BP 96 RON unleaded petrol, and used my favourite oil – K-Mart’s own brand, KMX 20W50. I use this oil in all my motors, for running-in and tuning, whether it is a high-revving Ford BDA, or a 500hp V8, and I have never had any problem with this oil.

The distributor is a Lucas 29D, with the advance stop welded up to give 7 to 8 at 3000-3200 rpm. The total advance for this engine is 26 to 27 , which means it had a lot of static timing. I find this a lot better because it allows the motor to idle off the advance, which means you can close off the carburettor butterfly further. This in turn helps the motor to shut down and not run-on, when the ignition is switched off. There is one drawback, though – you do need a good starter motor, as the old Lucas standard one doesn’t have enough horse•power for the job.

OK. Moving onto the dyno. First, we tested some of the more popular types of extractors and exhaust pipes. With the motor run-in, I had to choose an induction setup that I knew would make good torque and horsepower. I selected my 5.25” Weber manifold, and a 45mm Weber with 34mm chokes. (I know we’re mixing metrics and imperial here, but that’s just the way they are.)

Project Small Bore 3
45mm Weber on RE manifold

After sorting out the jetting, with the water temperature set at 80 C, oil pressure 80psi hot, air temp 22 C, humidity 50%, and barometric pressure at 29.85, the correction factor was 1.003. After a bit of testing of different exhaust pipe and muffler setups, we settled on a pipe with 1 ” Outside Diameter and 1 ” Inside Diameter, a 16”-long muffler with 2” ID, and a full-length back pipe – to simulate a full system on a Mini. The five sets of extractors we tested were, in order, Big-bore LCB (long-centre-branch), Maniflow Free Flow, Medium-bore LCB, Big-bore 3 into 1, and Small-bore Supa Pipes 3 into 1. See Table 2 for all the figures.

Table 2

                       Big LCB             Free Flow           Medium LCB      Big 3 into 1           Supa Pipes

RPM            lb/ft hp            lb/ft hp              lb/ft hp               lb/ft hp                lb/ft hp

3000            79 45               70 40                  79 45                   78 44.5                82 47

3500             80 53              71 47                   81 54                   80 53                   82 54.6

4000             80 61              75 57                   80 61                  81 62                    84 64

4500              82 70             80 68.5               80 68.5              81 69.4                  83 71

5000              82 78              79 75                   80 76                 80 76                    84 80

5500              82 86              79 83                   81 85                 80 84                    85 89

6000              81 92.5            75 86                  76 87                 75 86                     81 92.6

6500              70 86.6            68 84                  70 86.6               68 84                 73 90.5

Project Small Bore 3_3

 Project Small Bore 3-4
Maniflow Free Flow

Project Small Bore 3-5
Medium LCB

Project Small Bore 3-6
Big 3 into 1

Project Small Bore 3-7
Supa Pipes

Being tested first, and a popular choice for Minis, the big-bore LCB set a standard to measure against. The Maniflow extractors were very interesting, dropping a lot of torque down low, but starting to pull back good figures at the top end. The medium-bore LCB, took a big dip in power at 6,000rpm, compared to all the other manifolds, which surprised me a bit. No matter how many times we tried it at that rpm, the result was always the same. I originally wasn’t going to test the big-bore 3 into 1, because I thought they were far too big for this engine. To my surprise, they made very good torque down low. The small-bore Supa Pipes are Australian-made, have a very small diameter pipe, with a special collector, are all Mandrel-bent, and produced the best results. The figures were all quite good, but in one way I am a little disappointed with the results, as they did not really show up the advantage of the smaller pipes on the small-bore engine, which I expected. I should have built the engine with only around 60-70hp, as the medium-bore LCB do perform better than the big-bore pipes, from my experience, on the smaller horsepower engines, but I have found the Super Pipes superior on small engines. As the Supa Pipes gave the best results, we will use those to standardise the results for the induction tests (Table 3).

TABLE 3 – All tests done with the Supa Pipes extractors. Note: hp figures not corrected 

                   40mm Weber           40mm Weber              45mm Weber          45mm Weber
34mm chokes            34mm chokes             34mm chokes         34mm chokes
Redline manifold          Swan Neck             Redline manifold    RE 5 ” manifold
RPM            lb/ft hp                       lb/ft hp                         lb/ft hp                     lb/ft hp

3000             77 44                           78 44.5                         77 44                          82 47
3500              80 53                          80 53                           80 53                          82 54.6
4000              79 60                          80 61                           79 60                          84 64
4500              80 68.5                       81 69                           80 68.5                      83 71
5000              80 76                          80 76                           80 76                          84 80
5500               77 80.6                      76 79.6                        80 84                          87 89
6000               72 82                         70 80                           75 86                          81 92.6
6500               65 80.5                      65 80.5                        68 84                         73 90.5

Project Small Bore 3-9
45mm Weber on Swan Neck manifold

Project Small Bore 3-10
Twin 1.25” SUs on std manifold

Project Small Bore 3-11
Twin 1.5” SUs on std manifold

Project Small Bore 3-12
1.75 ” SU on RE 7” manifold

 RPM             Twin 1.25 ”              SU Twin 1.5”             SU Twin 1.25 ”        SU Single 1.75 ” SU
Std manifold             Std manifold               6” manifold              RE 7” manifold
lb/ft hp                       lb/ft hp                        lb/ft hp                         lb/ft hp

3000               81 46                           81 46                             81 46                           83 47
3500                80 53                          81 54                             82 54.6                       85 56.6
4000                76 58                          76 58                             84 64                          86 65.5
4500                 78 67                          79 68                            83 71                           87 74.5
5000                 77 73                          79 75                             86 82                          90 86
5500                  75 78.5                      76 79.6                         85 89                          87 91
6000                 69 79                          78 89                            77 88                          83 95
6500                  65 80.5                      67 83                            72 89                          76 94

Project Small Bore 3-2
Some of the carb/inlet manifold setups that were tested (not to scale)

Starting with the Weber carbs, I tried four different combinations: 40mm with 34mm chokes on the Redline 4.5” manifold, and on the Lynx Swan Neck (these aren’t made any•more, but there are still quite a few around, and there are similar manifolds from other overseas brands available). Then I tried the 45mm with 34mm chokes on the Redline 4 ”, and on my own RE 5.25”. Although the RE gave good results, I think this manifold is too big for the small-bore engines. It has too much volume for a road engine, in so far as part-throttle driveability goes. The Swan Neck is a manifold that a lot of people like to run down, but for the small bore road engines, making up to 90hp, it works very well. It has excellent throttle response, because of the small volume and high air speed, and is a very good manifold for road car use, with the 40mm Weber and 34mm chokes. However, it is not really suited to the 45mm Weber. The Redline manifold, with 45mm Weber, was very good. With a bit of grinding down on the manifold face, this manifold would have matched my RE manifold on this engine. A fully-ported one of these will stop at around 125hp, and has excellent driveability on the road. The 40mm on the Redline gives excellent driveability on a road car. You will notice the photo of the ram tube and the machined venturi, which both gave the same results. However, with the ram tube I had to go one set richer to match the machined venturi.

Now, looking at the SU carburettors.

Project Small Bore 3-14
My gyzmo for checking the SU slide. Note the large radius machined on the mouth of the carb. I find this as good as, or better than, ram tubes.

Before we start, you will see the little gizmo I made up, to measure how far the slide is lifting, when you can’t see the slide itself. All you need is a bar or tube of steel alloy, or wooden dowel. I’ve marked rings at 1/8” apart. Strap a pointer to the bell of the carb, and line it up with the top ring on the bar. As the slide rises, you can simply count off the number of rings to see what part of the needle your engine is running on. This is excellent for part-throttle openings, and I use this setup on engine dynos and drive-on dynos. It’s bit hard to use when driving on the road though! To set the standard this time, I used the standard Cooper S twin 1.25” SU setup. These proved to be a lot better than I expected, considering how short the standard manifold is. What was most interesting, though, was that we couldn’t improve on the standard air-box arrangement – BMC knew what they were doing here, for sure. With the twin 1.25” SUs on the standard manifold, we had to do a bit of fiddling around, trying various needles, to get the mixture right. We ended up with No 7 needles for the best results on this engine. These carbs did not have ram tubes or a standard airbox, but a radius had been machined on the front of the carbs. We then tried the twin 1.5” SUs on a 6” manifold, which was a setup we used on the Mini 1000 racing cars about ten years ago. These worked really well once again, and I thought they would come out on top. They really don’t fit on a road car, without a lot of body modifications, but I thought I’d throw them into the mix, to illustrate what I was saying in the last article about longer manifolds being better.

The next setup was with a single 1.75” SU on my long (7”) manifold, which has a very large volume at the carb face and leads the carburettor into a long runner of the right shape and size. We had a lot of trouble getting the right needle for this setup, as the slide was fully up by 3,500rpm, and stayed there until we shut-off at 6,500rpm. A single 1.5” SU was a waste of time on this engine, as it was just too small and could not supply enough air for this setup. But, it will work fine on smaller horsepower engines. Two other manifolds I didn’t try were the standard cast manifold, cut off the exhaust (it simply didn’t fit over the exhaust pipes), and the Mini Spares 1.75” competition manifold. I’ve tested the Mini Spares manifold in the past and found that it works very well, is easy to fit, makes good horsepower, has good volume and have no problems fitting air-cleaners. However, I didn’t have one available for this test.

Summing Up I think I made one mistake with this engine, in so far as it made too much horsepower. This meant it didn’t show up the differences between the big-bore and small-bore extractors, as I think would have been much more obvious on a motor that gave 60-70hp. When choosing extractors, you can’t go past the small-bore pipes, medium-bore LCB or 3 into 1 small-bore. On the dyno, running the motor at and throttle, by putting a stop on it, the small pipes do make more power and have better throttle response, which makes for better driveability. With inlet manifolds; if you want to run a Weber carb, my choice would be the Redline 4.5” or the Swan Neck. These manifolds on the small motors have very good throttle response, are easy to fit an air-cleaner when in the car, make good power and are good value for money.

Project Small Bore 3-13
Swan Neck manifold – a good compromise

If, like me, you prefer SU carburettors, then I reckon there is nothing quite like lifting the bonnet and seeing a well set up pair of SUs. If you are going to build a motor around 60 to 70hp, I would stick with the 1.25” twin SUs. I would rather see a better manifold, a little bit longer. If you are going to run a single SU manifold, you have a few choices. Firstly, you can cut the original cast one off the exhaust and use this. If it is a late model one, then you can use any SU carb, from 1.25 ” to 1.75 ”, with good results. If you use a Mini Spares, Maniflow or similar, then stick with the big-bore one. There should be no problem fitting any of them, even with an air-cleaner.To fit the Russell Engineering manifold, you will probably need to do some body modifications, depending on which carburettor you use – HS6 or HIF – and you will only be able to use an offset-type air-cleaner.

I would like to make special thanks to the following people, for their help with this testing. Greg Brown from Karcraft Australia, for supplying the extractors for testing. Greig Malaure from Mini Classic, for all his work in changing very hot exhaust systems, while I had to spend time answering the phone and making the cups of tea! And a big thanks to all the people who loaned me carburettors and inlet manifolds.

Project Small Bore Pt2

Last time we started building a small-bore engine for maximum power. But there is no point having a good engine and putting the wrong head on it.

I’m going to use the 12G202 head, as these are the best to modify for our purposes. They are a bit smaller than the 12G295 or 12G206 heads, which gives you a bit more metal to play with when grinding. As far as a standard head goes, you can’t go past the 12G295 or 12G206.

I do not like the use of the 1275-type heads (12G940, etc) as these are too big for the small-bore motors. Yes, they will make the horsepower if you rev them hard enough, but I can still make more horsepower, with a better spread of torque, using the smaller heads.

The smaller heads have much better air-speed and better filling, which in turn produces a better spread of torque throughout the rev range – and it is torque that accelerates the car. When using 1.218” valves the 295 head flows the same as the 940 head with 1.3”, but the 295 head is doing it with smaller volume right through.

To give an example, let’s look at the 970S and 998 Cooper motors. The 970S uses a Mk1 Cooper S head, with smaller combustion chambers – therefore higher compression – and larger inlet valves. Both engines make the same torque – 57 ft lbs – but the 998 Cooper engine makes this at 3,000 rpm, while the 970S engine makes it at 5,000 rpm – some 2,000rpm higher. My point is, bigger is not always better.

Formular jr1  Formular jr2

The Cooper Formula Junior head, showing (from left to right) the combustion chambers, and extra head stud holes.

As an aside, there was a one-off type of engine, of which only around 40 were made, built for John Cooper’s Formula Junior race cars. It is not well known, but worth having a look at. This was based on a 950cc A-series block, with a bore of 2.661” (67.6mm) and stroke of 3” (76.2mm) – giving a capacity of 1095cc – and produced 98 hp at 7,800 rpm with a 40mm Weber. The first version used a smaller cam and twin SU carbs, and produced 94hp.

It was dry-sumped and had special rods, but the best part was the cylinder head. This engine had a small-bore head (with two casting numbers – AEA626 and 12A185) which was almost the same as the 12G295 head. But, it had slightly bigger valves (both inlet and exhaust). More importantly, it had two extra head studs, one at each end, like the Cooper S heads, to prevent blowing the head gasket.

Getting back to our project motor, I have modified the combustion chambers on our 202 Head, ported it out and fitted bigger valves – 1.280” inlet and 1.062” exhaust. Be careful not to overdo the porting. You don’t need to go any bigger than on a 12G295 head. In fact, with a bit of cleaning up of the inlet ports, the 202 head is ideal for a road car.

Grinding Comb polishing Comb

Grinding out the combustion chamber (left) and polishing it off.

12g295 Std



Std 12G202

12g202 Mod

Modified 12G202

With a decent manifold and 1.75” SU carb fitted, this modified head has a good high gas flow of 115 cubic feet per minute (cfm) @ 25”, compared with the standard head at 70cfm.

This brings me to the importance of a good manifold. It is no good having a well-ported head and then putting a poor-flowing manifold on it, as the manifold is really just an extension of the inlet ports. If the manifold doesn’t flow efficiently then you have just wasted time and money on doing the head. I’ve seen some manifolds drop the airflow of a good Cooper S head by as much as 20%.

The length of the manifold is also a consideration, and here longer IS better. In this I am talking only about the length of the manifold. Don’t think that long ram tubes fitted with a short manifold will be as good, because they won’t. The critical length when dealing with carburettors is the distance from the valve to where the fuel enters the air-flow. This, of course, is not the case with fuel-injection.

So, the two things you need for a good manifold are length and volume. The Weber manifold and SU manifold that I make are both a tight squeeze under the bonnet, but they are designed for performance, not looks. My Weber manifold is about 5.25” (133mm) long, but has a very large volume for its size. My SU manifold has both volume and length – around 7” (178mm) along the centre-line of the manifold – and makes good torque on any size engine.


RE7 Weber

The old “Swan-neck” Weber manifold is disliked by many people, but it is actually not a bad manifold, if you are not after maximum torque and horsepower. So, if you are wanting a nice, mild engine, you don’t have to put the same type of manifold on, that you would use if looking for say 150hp. I’ve seen 90hp with these manifolds, which still makes for a lively road car.

Colin Dodds from Sprite Parts in Castle Hill recently tested five of the most common manifolds for Weber carburettors on a flow bench, then compared the best three with a Maniflow and my SU manifold while mounted to the head. Following is Colin’s report, reproduced with permission.

We regularly get asked what is the “best” Weber manifold to fit to your A-series engine. I’ll admit, I’m biased, and I do have a favourite, but largely it also depends on what you want to define as “best”. Certainly “best” has to include “fit for the purpose” and in that context you have to consider whether the manifold actually does fit. Some manifolds made for Sprites and Midgets don’t really fit a Mini, and some made nicely for a Mini don’t produce the best results for a Sprite/Midget.

Anyway, a little bored and wanting some concrete statistics, I gathered up all the manifolds I could find and wandered off for a scientific test on a flow bench. For the purpose of this exercise, I will define “best” as the one that produces the highest cfm (cubic feet per minute) of airflow at a partial vacuum of 25 inches of water (which I believe is the “standard” of measurement).

Now, let’s start with a little theory (sorry).  Engines need fuel and air mixed in the correct ratio to ignite efficiently, and the more of this mix you can deliver to the engine, the more power the engine is theoretically capable of producing. The actual power output of the engine depends of course on many more factors which will include cylinder head design, camshaft profile and timing, valve size and lift, exhaust system, and compression ratio. A fairly standard 948cc engine might produce maximum power using only a moderately effective carby and inlet manifold. However, as your engine increases in capacity and performance capability, so it needs more fuel/air to enable it to produce the best results. So it is fair to say that the manifold that flows the most air, is CAPABLE of producing the most power.

We had five manifolds on hand, and I know this doesn’t represent all the ones available world-wide.  However, they would be the ones most used in Australia. They can be described as follows, but sorry if I don’t include your favourite manifold (nope, no Cannon ones were available).

Man A: LYNX Mini manifold, steeply upswept “swan-neck”. Fits easily in a Mini, which is why it was designed that way.

Commonly accepted as a poor performer.

Man B: LYNX flat 5” A-series manifold. Fits a Sprite or Midget, will not fit a Mini without cutting a hole in the firewall.

Man C: Warneford or Redline 5” manifold. Upswept to clear the firewall of a Mini, also fits nicely in a Sprite/Midget.

Man D: Warneford or Redline 6” manifold, longer (duh!) and not so upswept. Needs firewall modification to fit a Mini.

Weber comes VERY close to the inner mudguard on Sprite/Midget.

Man E: Limited-production hand-finished 5” cast manifold from Russell Engineering.

Fits comfortably in either Sprite/Midget or Mini.

And so to the results of the shoot-out.

Man A: (LYNX Mini) – 104 cfm

Man B: (LYNX 5”) – 136 cfm

Man C: (Warneford 5”) – 139 cfm

Man D: (Warneford 6”) – 175 cfm

Man E: (RE 5”) – 207 cfm    (Russell Engineerings SU manifold was independently flow tested in the UK)

I had two people suggest that we re-run the tests, but this time with the manifolds attached to a cylinder head.  That way we could see the extent to which the manifolds hindered air flow into the head. Well, that sounded like a really good idea, so that’s just what we did.  We grabbed a nicely modified 12G940 head from a 1275cc engine, with good porting etc, and 1.4” inlet valves, set it up on the flow bench, and took readings with and without manifolds.  We didn’t bother testing the two poorest performing manifolds as we really weren’t interested in the result.

I have to admit, the results weren’t exactly what I was expecting. I knew the raw numbers would change, but I wasn’t expecting any change in the order of ranking of the manifolds – but that is what happened. We re-ran the test just to check, and nothing changed.  All tests were done with the same vacuum as previously, and with .500” of valve lift.  That’s about the lift you would get with a performance camshaft and 1.5:1 rockers.

146 cfm through the head alone

144 cfm (2 cfm or 1% drop) with the RE

131 cfm (15 cfm or 10% drop) with the 6” Warneford/Redline

130 cfm (16cfm or 11% drop) with the Maniflow

113 cfm (33 cfm or 23% drop) with the 5” Warneford/Redline

Just for the hell of it, we also attached the RE single SU manifold, and it flowed 141 cfm (5 cfm or 3% drop).

flow bench flow bench2

And that was WITH a 1.75” SU attached to the manifold!




RE7 Weber

Now, nothing sounds quite like a Weber, but there are more important things than how it sounds. You can still get the same horsepower from an SU, but for racing conditions a Weber is more drivable. For normal road use, even if you are a bit of a “Boy Racer”, the SU is great. It is also a lot quieter than the Weber, possibly more economical and a lot less smelly, which is all the better if you are driving your Mini a fair bit. Still, if you really have to have that Weber sound then there is no comparison.

It is very important to remember what you are building the motor for. If it s going to be a daily driver, or used for weekend cruises, then build it for that. Don’t go overboard with a big head, lumpy cam, manifold and exhaust which would be more suited to a race engine. Instead, aim to get a good spread of torque from low down. It will be much better to drive than a motor which doesn’t start to make power until around 4,500-5,000rpm.

When I build race engines I still chase torque as the most important factor. Getting out of corners quickly and accelerating away is more important in most racing than outright top speed. When it comes to top speed in a Mini, I’ve done a lot of testing with a GPS (no chance for tacho, tyres or other variables to throw out the results) and, without a doubt, a Mini on narrow tyres and no flares, with 145-150hp, will not go over about 123mph on a flat road. But, a similar Mini with 115-120hp will still do 118-120mph.

This is because of the drag that is inherent in the design of the Mini body, and it takes a massive amount of horsepower to overcome this. Yes, Minis have recorded faster speeds at Bathurst, but that is on Conrod Straight, which is down hill! I would happily sacrifice 10-15hp in the interest of getting an extra 5-7 ft lbs of torque.

So, with our head complete, and our choice of manifold sorted out, we need to look at fitting the head and setting the valve timing. As I mentioned in the last issue, when timing the camshaft I always have the head fitted, to put tension on the chain or belt.

Before fitting the rocker gear, I’ll make a quick point on what sort of gear to use. Unless you are looking for power above 5,500rpm then do not use rockers with a ratio greater than 1.3:1, as they will cost you power and torque. When fitting the rocker gear, make sure that the rocker pad is centred on the valve tip when the valve is on half lift.

Now, with the head on the engine and the rocker gear fitted and adjusted, it is important with a performance engine to get the valve timing the same for all valves. By this I mean, when the valves actually start to open, and it has nothing to do with ignition timing.

To do this we need to use a dial indicator on the valve cap and a degree wheel on the crankshaft. With number one cylinder at Top Dead Centre (TDC) on the firing stroke, set the pointer on the degree wheel to Zero.

Now, rotate the engine and check the opening point on number one valve. That is when the dial indicator just starts to move by about one-thou. Repeat this process for the other three inlet valves.

You may find that three of the valves open at say 35    Before Top Dead Centre (BTDC), and one opens at 29    BTDC. This often happens with Mini rockers, both standard and after-market. You may get a bit of a shock when you start checking them.

To get the 29   valve to open at 35   you may have to close the tappet up, so that it is set at say 0.012” rather than 0.016”. Don’t worry about the difference in settings as it is more important to get all the valve timings the same.

On some big-power engines I’ve had tappet clearances vary from 0.015” to 0.023” on the one engine. Remember, get the valve timing the same and you will make more power.

If you are a little surprised about this variance, remember there are four factors that can change the tappet clearance. These are the radius on the cam-followers, the length of the pushrod, the length of the tappet adjuster and the ratio of the rocker.

I can’t stress enough the importance of getting these valve timings the same. A difference of 0.002” can mean a loss of three to four ft lbs of torque across the rev range.

timing wheel measring

With degree wheel set to 0 (left), rotate engine until valve opens one thou (0.001”)

The ratio of rockers is also a bit of a concern. As I said, unless you after power above 5,500rpm, there is no need to use greater than 1.3:1.

Some rockers which are sold as 1.5:1, both roller rockers and forged rockers, are actually measuring 1.6:1 and higher. This creates a lot of problems with valve timing and lift.

Some cams I am aware of are giving 330 duration, instead of the nominated 280, and instead of the rated 0.480” lift have 0.520” – 0.530” lift. This is because the rockers are a higher ratio than stated, so are accelerating faster onto the valve, which in turn gives longer duration and higher lift. This can be corrected by opening up the tappet clearance.

I have found that with 1300cc – 1480cc A-series race engines you don’t need more than about 0.480” – 0.500” lift, and with small-bore engines, like the one we are looking at, 0.400” – 0.450” is adequate.

So, now we have the head on the engine, the rocker gear and valve timing sorted, and we’ve decided on the inlet manifold and carburettor.

In the next post we will be putting the engine on the dyno and running a series of tests with a variety of exhaust extractors, inlet manifolds and carburettors, and should be able to prove most of the things I’ve mentioned this time around. Following that will be the post on the 2014 Small bore build to see what has changed and developed over the years.


Project Small Bore

A few years back Russell Engineering built a small bore project motor and wrote an article for The Mini Experience Magazine.
Below is part one of the article and in the following weeks we will be posting the next two parts. The reason for bringing these articles up  again is that Russell Engineering is in the process of building a new and some may say improved small bore which will feature a few of the new products, such as the 68mm Small Bore Pistons and threee new Camshaft to try. These previous articles will be referenced to, for the new build as some things have changed and some have stayed the same. Stay tuned, read on and enjoy.

Small Bore Project Part 1

We all long for the power and torque available from a 1275cc engine, but with these becoming more expensive and harder to find, we’ll take a look at the alternative of getting some decent power from the small bore engines.

For the price of a good 1275 crankshaft you could buy two or three small-bore motors. The cost of reconditioning a small-bore block isn’t going to be a lot less than doing a 1275cc, but the cost savings on parts like the crank alone would go a long way towards modifying a 998cc or 1098cc motor. Over the next few issues I’ll look at how to get the best results from an 1098cc engine. The bore for the 998cc and 1098cc engines are the same, but the 1098cc, with its longer stroke, will produce a better spread of torque across the rev range. If you wanted to do a 998cc the process is much the same. The engine will not give as good a torque figure, but it will rev more freely at the top end. In this issue we will take a look at what we can do with the block, crank, and camshaft, pistons and rods. I’m going to assume that if you are intending to do this type of work, then you probably already know your way around the motor fairly well, and you will already have the engine stripped down. However, before removing the old main bearings, check that the oil holes in the block line up with the holes in the main bearing shells.


If not, the block will have to be ground out to match its oil passages to the bearings. Starting with the block, it should be chemically cleaned to remove as much of the rust and rubbish from the water ways and oil ways as possible. But, don’t forget to remove the two oil gallery plugs first to ensure everything that can be is cleaned out. Now, there is a cost-effective way to get rid of all the rust out of the block (and the cylinder head too) without any special high-tech tools. Simply mix up a solution of molasses and water (one part molasses to three parts water) in a plastic tub. If the mix is too thick to get into the water ways easily, you may need to thin it out a little with more water. I used to use this method and it worked very well, but when the aluminium bung in the tub disintegrated – molasses eats aluminium the result was very messy! Nowadays I send my blocks and heads to Redi Strip in Blacktown (Sydney). It costs over $100 to have a block chemically stripped, but the results are fantastic.


This block has been cleaned with the molasses bath.Photo 3: Line the hole in the crank up with the groove from the bearing shell. Photo 1: Here the oil hole in the bearing shell doesn’t line up with that in the block. Just submerge the head or block in the solution for about three or four days. Take it out and hose it off. If all the rust isn’t gone, repeat the process. One thing to remember is that it will not remove paint, grease, carbon, dirt or anything else, but the rust. With our project motor I’m going to bore the block +0.040” (40 thou’) oversize. As we are not going down the forced-induction path, we will be running high compression pistons I like to run around 10.5:1 for more power without sacrificing reliability. Now, you could go out and buy some special flat-top pistons, but part of the point of doing this motor is to save money. If you use the standard 998cc pistons, you can machine off the 0.140” crown, to get flat top pistons much more economically. With the block cleaned and bored, and the pistons sorted, the next step is the crankshaft. Remember how those oil holes in the block didn’t line up (as is usually the case)? Well, neither do the holes in the crankshaft. It is important for the holes to be moved over so they line up with the grooves in the bearing shells, to ensure proper lubrication under the extra power we will be feeding into the engine. The standard arrangement is fine for a standard engine, but not up to scratch for what we are doing. To align these holes I use a little dremel, or die grinder, to lead the oil from the bearing groove directly into the oil hole in the crank.


With this modification, it is not necessary to cross-drill the crank if the bearings have a full-circle groove around them. In saying that though, I always cross-drill my cranks that are going to be used in race motors. You may have heard the term wedging the crank. Well, there is a right way and a wrong way, and simply grinding off metal to form a blade is the wrong way. The metal removed from the web must only be removed back as far as the crank pin.


Only remove metal from around the pin area, as shown at the bottom part of the photo. This will improve the harmonic balance of the crank. Do not blade the crank, as we need as much weight as we can get on the outer end of the web to counter-balance the weight of the piston, rod and crank pin.


(Left to right) a Russell Engineering billet crank, a correctly wedged and balanced standard crank and an untouched standard crank.

When balancing the crank, only remove metal from the pin area, not off the web. We are trying to improve the harmonics of the motor, and there is a big difference between dynamic balance and harmonic balance. A good example of this is in an article by the manufacturers of Schenke balancing machines, where they took a Mercedes crank, cut all the counterweight off and balanced it dynamically. They then put it in the engine and ran it. The noise levels were way up, but power was way down, and it nearly shook the motor to pieces, because the vibration level was so high. This was an extreme case, but illustrated the importance of balancing harmonically. BMC were one of the worst offenders. I’ve seen Cooper S cranks that have had about 3/4 of the centre counterweight removed to get the thing balanced. And they did it with standard 998cc and 1098cc cranks as well. In a case like this, you need to weld up the counterweight and regrind it, then remove the weight from the other end. Next are the connecting rods. These can be a real problem, due to inconsistencies in their heat-treatment. When I started Mini 1000 racing we had a few rod failures, breaking just above the big-end. I measured all the broken rods and found they all measured around 18 to 20 Rockwell C hardness, while good ones measured around 23-25 Rockwell C. I then had all my rods treated to 30 Rockwell C and no more problems! Don’t have the caps heat-treated though, as they tend to open up with the heat and then don’t give a good fit. Also, make sure to remove the little end bushes from the rods before heat-treatment. After treatment, the rods can be lightened by machining the sides. You can take 0.150” off both sides (photo 6). Now to the camshaft. There are many cam grinders in Australia and overseas. They all have their favourite cam, and they all believe their cams are the best. I’m no different, and in this motor I’m going to use my favourite cam – the RE13. This is a sports cam and a good all-round cam for performance in a road car, but not what I use in a standard road engine. And it is not a scatter cam. Just an aside if you think you know who first came up with the scatter cam, you are probably wrong. It was first developed right here in Australia, by probably our greatest race engineer, Phil Irving. In his book Automobile Engine Tuning (first printed in 1962 by Pitman) Irving refers to scattering lobes in motors with Siamese ports. I’ve been told that he was playing with this type of cam back in the late 1950s with BMC engines and Holden Grey motors.


Big-end of conrod showing where it has been machined 0.150” George Wade of Wade Cams was grinding scatter cams for Peter Manton in the early ’60s. When Clive Stenlake joined George Wade in about ’65 or ’66, he was grinding the ever-popular 285-CO and 176-0 cams. Clive left Wade Cams in 2001 to start his own business, Clive Cams, and is still grinding these cams today. Getting back to the RE13. This cam pulls strongly from 2500-2700 RPM, and runs through to 7000-7500 RPM, making strong torque and horsepower. So, as I said, it is a good all-round cam.


RE13 cam on the grinder.

Now it is time to assemble the block. First, do a dummy assembly and check the deck height, making sure the pistons are flush with the top of the block at Top-Dead-Centre. Check the main-bearing clearance with a Plastigauge. It should be between 0.0015” and 0.0025” (one and a half to two and a half thousands of an inch) for a performance engine. Ensuring all parts are nice and clean, we can now go ahead and do the final assembly. When fitting the oil gallery plugs, use a little bit of Locktite – just to be sure. Two items that I consider very important in a Mini engine are the crankshaft end float and connecting-rod side clearance. The old thrust bearings can often be cleaned up with some wet-and-dry paper on a sheet of glass, to get 0.005” to 0.006” end float. This will give enough clearance to get the oil flowing in and out, to avoid overheating the oil, which would damage the main-bearing. We also need enough clearance so that when the crank flexes on that accidental over-rev and believe me, they do flex it doesn’t grab the thrust bearing. I have found that where the numbers are stamped on the back of the thrust bearing, they can raise up around 0.003”. This would give 0.006” over the total width, and this is enough to lock up the crank. So, make sure you check the width of the thrust bearings over the numbers as well as at each end. This can be rectified by rubbing on wet-and-dry paper to remove the raised edges of the numbers.


Raised stamp on thrust bearings.

Getting enough oil into the thrust bearings is very important too, and there is another trick here. I like to put a slight chamfer, about 1mm on a 45 degree angle, on one edge of one main-bearing shell.


Where to chamfer main bearing.

Do this on the thrust side (the clutch side) of the main bearing, so it can squirt oil onto the thrust bearing. Give the conrod side clearance at least 0.010” for the same reason – to keep the oil flowing and prevent the crank from grabbing the rods. With the Plastigauge, check the conrod bearings have 0.001” to 0.002” clearance. I like to use Vanderval/AE Heavy Duty or ACL Duraglide bearings. If you are going to use aluminium-tin bearings, make sure your clearances are on the bigger end of the scale. Use a good quality assembly lube on the bearings and crankshaft. Don’t use lock-tabs on either the mains or rod bolts (as are used on the original motors). These are made of mild steel (very soft) and with high revs they compress, and lose tension. The result is spun bearings and a BIG bang! Always prime the oil pump with a thick assembly lube, or it won’t pick up oil when you first start the engine. Now the piston rings. If you are lucky enough to get a set of rings you have to gap (they are often made too small) aim for a gap of about 0.010”. When fitting circlips to the gudgeon pins on small-bore motors make sure they go in the right way around. Don’t laugh, it is a common problem and easy to get wrong. You’ll notice that the circlip has one rounded edge and one square edge – this happens when they are stamped out. Put the square edge facing out. With the wire-type clip, make sure they are a tight fit. If you prefer, you can replace the circlip with some Teflon buttons. When fitting the pistons into the bore, I only use a light oil – WD40 or similar – on the bores as you want the rings to bed in quickly. Never use friction-modified oil in assembly or running in, as the rings won’t bed in properly. I never use friction-modified or synthetic oils in Mini engines, because the oil doesn’t stick to the rockers, or the camshaft, when in motion, which causes wear. When fitting the camshaft, my rule is “new cam, new cam-followers”. Be careful to use only good quality cam-followers. For timing the cam, I use the “full-lift after topdead-centre (ATDC) method. This is more accurate, and I always have the head fitted to put tension on the chain or belt. If you have a camshaft but don’t have any setup figures, just split the overlap at Top Dead Centre (ie: inlet and exhaust valves open the same amount at TDC). To do this, use either full vernier gear or offset cam sprocket keys. That should be it for the block.


Part Two-We will look at the head, valve timing, manifolds and carburettors.

2014 Phillip Island qualifying in the RAIN!

This years Phillip Island saw a wet start to proceedings and qualifying in the rain makes for some fun times.

Graham qualified first by more than three sconds to the nearest competitor, but unfortunatly racing was not an option after breaking a rocker during qualiying.



Mini Racing

2014 has arrived and like every year, the workshop is busy with preparations for the racing season across a broad range of categories. I race currently in an Nb car and have been fettling both the car and motor, and I am still playing with coming into the first race meeting of the year. I’ll be updating my page soon with a run down on some of the projects I am working on. Bare with me, I will get there.

In the mean time have a look at the videos page for a link over to youtube of me running about in my at the time Nc car.

It was filmed at the mini 50 celebrations that were put on at Wakefield Park Raceway back in 2011. The car had a problem on the first lap so I pulled off to let the field go by before sputtering back to the pits. As I pulled back on the car cleared it throat and roared back to life. So I set about chasing the field down. Now that was fun!

Check back and hopefully I’ll have some more musings for you soon!

11 Stud/Bolt Small Bore Head

One of the problems with the small bore head when a lot is machines off the face, is they leak or blow the head gasket out the ends. So, this is how to convert a small bore head to an 11 stud/bolt setup.

Just a note on machining the face of the head. I never take any more than 60″ – 80″ off the face of the head as it flexes and warps to much and you end up losing more than you gain with gasket seal.

Back to the 11 Stud/Bolt set-up.

I take an old Cooper ‘S’ head, sit it on top of the small bore head and locate it in place with drills down the stud holes. Now take 7/16″ drill bit and drill down through the end of the head at the no.4 end. Remove the Cooper ‘S’ head and take a larger drill bit or a counter sink tool and put a large chamfer on the top and bottom of the 7/16th hole you had just drilled. We will come come back to this hole to finish it off after we drill the other end.

sb11stud2  sb11stud3

Now, take the Cooper ‘S’ head and place it gasket face to gasket face onto the small bore head, then locate it with drill bits again. Now take a drill that fits the hole in the Cooper ‘S’ head at the no.1 end and drill into the face just enough to mark it. Remove the Cooper ‘S’ head and drill a 1/4″ hole through the gasket face only. NOT RIGHT THROUGH the head. We will hold this end down with  1/4″ capscrew underneath the thermostat in the water way.


Ok, now back to the no.4 end. We have to make a tube 7/16″ outside diameter and 5/16″ inside diameter to go down inside the hole we drilled.

Make the tube the same length as the thickness of the head as it has to  be welded in. I brazed my tube in. To do this the head has to be pre-heated, so I just placed it on the BBQ with the lid down and warmed it up to 500-600 deg Fahrenheit or 260-315 deg Celsius.


The head will go a soft blue and with a very soft flame on an oxy torch, I filled the chamfer with brass with the tube in place. Turn the head over (It’s hot, so be careful) and repeat on the other side. NOTE. Use cast iron flux, not normal brazing flux. Once done, turn off the BBQ and put the lid back on and let the head cool down slowly.


After the head has cooled down, you can then machine both faces, top and bottom to clean them up.


Lets move on to the block.

Take the head and place it onto the block and locate it with studs or bolts, which ever you are using, and drill the block enough to mark the face. Remove the head and drill and tap the block with a 5/16″ UNC thread at the no.4 end and at the no.1 end drill and tap 1/4″ UNC thread.


When it is time to assemble the head to the block, you can use cap screws for both the new holes. The no.4 5/16″ cap screw can be tightened down to 15ft/lb, while the no.1 end I use a ball end allen key with a spanner on the end. This I tightened by feel, until the allen key starts to twist. because you are pulling down directly onto the gasket , you don’t need a lot of pressure.


There you have it. A small bore 11 stud/bolt head.


68mm Flat Top Pistons – Suit 998/1100

New product

68mm flattop piston to suit 1100/998 motors



These pistons are made of 11/12% silicon.These are a very strong piston and will suit race application. The weight comes in at 286g with pin and rings. The pistons are drilled behind the oil ring so there are no slots. the gudgeon pin is fed by oil from the top and the bottom. Being a flat top piston, dishes can be machined in if required.



Small Bore Cylinder Heads

Three Head Inlets
Click to enlarge

Ok lets take a look at the cylinder head. Here we have three small bore cylinder heads.
From left to right we have a AEG295 head (left). This is the performance head for small bores. The second one is the AEG202 (middle) and the third one is the 998 head (right). Now what i’ve done is cut them all through the inlet port to show you the difference in port size of all three heads.
Now the AEG295 head has the largest port of all which is really quite a big port for the size valve it uses. It measures 2.220″ high by 1.030″ wide the valve size is 1.218″.

The second one is the AEG202 it has an inlet port that measures 1.000 high by 0.937″ wide and the valve size is 1.156″.

The third one is the smallest one of all, the 998 head, of which there are several casting numbers. This has a round port (0.937″ in diameter), with a big chamfer at the manifold face which tapers from 1.187″ down to the 0.937″. You will notice that all three ports are a different core (the outside diameter).
Now because there are more 998 heads around than the 295 or 202 this is the one we will modify because it’s the smallest of all three. There is a little more work to get it to flow really well, but because there is more metal to remove there is more metal to get the shape right for better flow.
Now if you look at the 295 and the 202 inlet port you will notice that they have lowered the bottom of the port to open alot further than the 998, in doing this they have done away with the short side radius which is bad for flow at low lift and for high lift.
Now if we cut the port the right way it will be a really good flowing head.
Starting with the top of the port we have to angle the roof of the port down 1 degree from the manifold face towards the bottom of the port. Going square across the top of the port you can go as high as 1 3/16th diameter on the manifold face or 0.880″ from the rocker cover face to the top of the port. If you are doing this on a mill you can use a 7/16 diameter end mill long series going in to the depth of the flutes. In doing this it is going to leave a step where the end mill finishes. This is where you will have to blend it in to the roof of the port. Have a look at the photo.

Port Milled out

Milled out ready blending

Modified 998 Port

The second photo shows the port after it has been blended in.

Now for the width of the port you can go to within 1 millimetre or 0.040 from the pushrod holes. As for the bottom of the port, that has to be angled up at 3 degrees. Now with this you cannot go to the diameter of the 1 3/16th chamfer. From the rocker cover face to the bottom of the port measures 1.750” These dimensions are a guide only of most of the heads i’ve measured. They are not quite all the same but are close to the same so be careful.

Hold back a little if you are worried about going through to the water jacket,as you can see in the photo the 998 head has a lot more metal on the bottom than the others but the smaller port will still work very well with these dimensions. The port is still bigger than the 202 head but not quite as big as the 295 head. This size port will give a very good velocity as well as volume for good filling of the cylinder.

Std 998 Port

Standard 998 Inlet Port

Manifold Face

Modified 998 Inlet Port

Re-Seating the Valve and Throat Area

Ok lets cut some seats now. If you have a look at the 295 head you will notice that it has a very narrow seat 0.040” wide or 1mm, that’s fine but the bad part is they just made a hole straight down from the seat. They have a valve of 1.218″ diameter and a throat diameter of 1.170″. This is 96% of the valve diameter, which is a little bit big for a good flow at low lifts and high lifts. I’m going to use a 1.260” diameter valve and a throat diameter of 1.008”. This gives us a throat diameter of 80% of the valve. I sometimes go down to 78% of the valve, by doing this it helps accelerate the air out and around the valve as we are creating a venturi shape under the valve. Have a look at the photo and you get the idea and it’s very easy to blend the throat into the port area.

Valve open

Valve Closed

Now on the short side radius you can get a really nice short side radius because you have a lot more metal to play with, unlike the 202 head and the 295 head. This gives you a really good throttle response out of corners and on part throttle openings. Now to get this throat diameter I use a full radius cutter that I have developed because of the small valve diameter and the siamese port they need a different type of radius to other types of cylinder heads. I also have 3, 4 and 5 angle seats that work very well.

Five Angle Seat

But I find it easier to get a better short turn with a radius cutter.
Now because the mini has a port 90 degrees to the valve it is very important to get the air turned to come down onto the back of the valve and flow around the whole diameter of the valve and not just flow across the back of the valve. The difference between a good short turn and a bad one is huge. Now with the divider, because of the small choke area you can get a really good fat radius around it to help with flow.

The Combustion Chambers 

The combustion chamber you must get rid of some of that peaks it shrouds the exhaust valve causing it to overheat and burn out, which also leads to cracking the exhaust seats and chambers. The shape that I have come up with works really well.

Chamber Shapre

This chamber has been CNC’d


Photo of an exhaust insert fitted to a 295 head. Valve size 1.070″ Throat diameter is 83% of valve diameter. Note, the full radius and top cut.

You need to take next to nothing away from the beak-side once you have cleared the inlet valve as the air is being fed from the centre of the cylinder. Have a look at how the air is leaving the cylinder and at the angle of the port to the chamber.

Minis have a very efficient exhaust port, you can grind a little away on the spark plug side to help angle the air towards the port. As for the seat itself, I like to use a good top cut and leading into a good full radius seat with at least a 83-85% choke area of the exhaust valve. On the small bore heads they have quite a large area compared to the choke area, you don’t need to grind much out of the exhaust port itself just give it a good clean up. Most of the time I use a 1.070″ diameter size valve. On the centre exhaust you can grind the guide boss away but be very careful when grinding it away you will notice to the left and right of the valve guides there are 2 hollows. Do not try to grind the centre of the boss down to their level, because you will find water! Be warned!
Here is a photo of the exhaust port number 4.

Exhaust no4

Now this is using a standard 1.00 valve and note the choke area is not under the valve but around the guide boss area which is still smaller than the area of the exhaust port. Also note how close to water is getting, don’t grind too much or you’ll get a little thin. 1.070” is a very good size, as you can get a lot of air through a valve that size. For an all out race head I never go bigger than 1.125″.

Here are some photos of Standard exhaust ports. Note, 295 exhaust ports and valves are the same as a 202.

998 end

Std 998 End Port


Std 998

202 end

AEG 202 End Port


AEG 202 Port

Below are two photos of the centre port in a 1275 12g940 head that has been modified for full race. These will give you a good comparison between small and large bore porting.



Inlet Ports

Three Heads

The photo above features a 295 head showing how they dropped the bottom of the port to get the port volume. In doing so they sacrificed the short turn radius and the air is going to flow across the back of the valve and not the whole diameter of the valve head. Note how they machined the throat area, the valve size is 1.218” diameter, the throat diameter is 1.170”. That leaves 0.024” to cut the seat on which gives you about a 0.040” or 1 millimetre seat. Note the throat diameter is 96% of the valve which is a bit big. But note how they have done it, they dropped the bull nose cutter down to blend into the radius where the guide is, then they have dropped another cutter down to get the throat diameter.


Bull nose cut on throat

295 Valve

295 head with valve fitted standard

But they have a gone down 90 degrees to the chamber roof, which is not going to help the gas get out, it is going to crash into the back of the valve. Now have a look at the throat in the head I did.

Valve open

Valve Closed

Valve Seat 2

Three angles on the valve
Have a look at the valve at low opening and you will see how the air is helped to get out by the shape of the radius.

With the 202 head they use a 1.156” diameter inlet valve and a throat size of 1.000” which gives it a throat diameter of 86% of the valve and the same percentage for the 998 valve. With this you can start to get a better seat shape which would be better than just a 45 degree that they had as standard.

With these small bore heads it is really necessary to use the longer valves, 1275 type length, as you have a better choice of springs and less chance with coil binding with sports and race camshafts. But in doing so it will be necessary to pack under the rockers to get the rocker angle correct. The way I do this is to have a rocker pad or roller in the middle of the valve tip at half valve lift. To achieve this, you possibly need about .0.100” or 2.5mm thick spaces. This is a good starting point to get you close.

To summarise, the 295 head is possibly the easiest and cheapest way to get better performance out of a small bore motor. But for an ultimate performance small bore head, it turns out the 202 and std 998 head is the best to modify. For an all out race head in the small bore class you can go to 1.280″ to 1.300″ inlet size. Any bigger than this and you start to run out of metal to create the correct shape.

Something that was quite interesting is that all three 998 heads that were cut still had casting sand present inside the heads. This is something that is difficult to get rid of after the casting wires are pulled and is also difficult to detect and rectify.

Casting Sand

In a future article will see some dyno figures for the various heads and combinations of inlet and exhaust port sizes.

Graham Russell