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.