crankcase pressures in a running engine?

[JohnL]

It's an odd question, but what are the pressures in the crankcase of a running 2 cycle? Looking for the maximum positive pressure when crankcase is under pressure from piston moving down, and maximum negative pressure (vacuum) when piston is moving up.

 

[timberwolf]

It will depend on the RPM, bore, stroke, intake timing, and base volume, but typical numbers will range from 1.4 - 1.6 atm (6-8psi) a bit before BDC down to .8 atm (-3psi) shortly before TDC.

With a pipe / tuned intake more pressure and vaccume can be had.