Oops

Maybe I misread the post? Vin did you want to know engine diameter? Then it is 3.5 " for the SimJet, RAM and PST. The exhaust tube on the other hand should be around 21 mm if used as a straight non tapered design. Tam probably has done the most testing here and his measurements are probably even more efficient. I think BVMs F86 pipe etc is roughly that diameter.

sorry boot that