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John Farrar

Fantastic Roger, Well Done!

Regarding the cylinder head shape, I have always felt that the std plug position/head shape is too much of a compromise: just look at the insensitivity to ignition advance.
The later “car” engine head shape/plug position seems so much more sensible.
Colin Heath and I stopped using full squish heads, even though we had no mechanical problems at over 15:1 compression ratios(22cc head volumes). We ended up with full squish on the exhaust with a large volume on the transfer side with an “encouragement ” space for the flame path where the deflector edge bisects the combustion chamber at TDC.This drops the compression to about 12.5:1 but the bike is at least as quick. This was an attempt to get to the “car engine head shape with the std plug position; I’d love to try a different plug postion.

Anyway congratulations once again ; I can only stand back and marvel at your continuing and amazing enthusiasm for these flawed, yet fascinating motorcycles.