Always run some type of evac system. The type depends on the application. One benefit is better ring seal. Crankcase pressure doesn't let the rings seal properly. And a vacuume can add h.p. Amount of vac you want in the crankcase, and the added power you will see depends on if your ring package was designed specifically for said vacuume.avomcd said:How can you tell if you need to evacuate pressures from the motor through the exhaust or with a pump. I run a big-block now with 11:1 comp and no evac system and it runs fine.