jensenracing77

i was going to put this in the clubhouse but it should apply to all gas engines. i am building a 4 wheeler that has stock 12.5:1 compression and runs on pump gas. i am going to go to 13.5:1 with a cam from a race engine builder. he said after i use his cam i can still run pump gas, even with this compression. he said that his cam has more duration and will lower the cylinder pressure and allow the use of pump gas. is there some place on the net or someone here that can help me understand how this works. if it lowers the cylinder pressure wouldn't that lower the compression? would this work for car engines? i figure that the high RPM that these engines spin may have something to do with it. they produce the power at much higher RPMs than a car engine.

tonycpe

About 185 .lbs of cranking compression would be about the limit to run pump gas , maybe 190 with aluminum heads.
My motor did not like 195 .lbs compression and pump gas .
Yes , More duration will lower cylinder compression and raise the power band rpm.