195, wow so it's safe to say you have reduced compression distance by raising the exhaust roof and have had to reduce the combustion volume to 1cc in order to have the adequate compression.

No. There is no compression until there is enough pressure behind the piston ring to push it against the cylinder wall. This has nothing to do with raising the exhaust roof. If you tested the compression for an exhaust timed at 175* compared to 195* at the same engine RPM, the numbers would be the same, providing the ring is good in both cases. I raised the exhaust only to increase the time area number necessary for high RPM power. It is easy to look a various compression numbers as the exhaust timing is raised & as the head button's volume is decreased by using a standard compression gage. At approximately 3500+ RPM the reading should be 165 to 185 PSI. Excessive lubricant can raise the reading. I usually check this after 14 to 20 full throttle runs on the engine.

JA

People have been arguing for decades about whether geometric or trapped (the compression after the exhaust port closes) compression ratio is correct. Who cares? The minimum head volume you can run without detonation on the fuel you are using will make the most power. I personally like to start with the geometric compression ratio because it doesn't change and confuse me when I play with different exhaust timing. The Japanese like trapped compression ratios. Two strokes are very complicated, mechanically simple engines. You can read about what I know in the three part series High Power Two Stroke Design starting in the November 2012 NAMBA Propwash . Most of the ideas in the series come from people who have a lot more two stroke experience than I do. I tried to show the past ideas and the developments that lead to the present, simple engines as well as possible future developments. The engines we run are a long way behind the best designs for high power.

Lohring Miller

PS Jim, thanks for crediting me with the surface plug idea. However, ideas are cheap and you did the work it took to make a working plug.