Crankcase Pressure

On my exhaust systems I run what I call a EVAC system. Basically this is a one way check valve I weld into the header right pass the 4/1 or 4/2/1, and then connect a rubber hose from the valve to the crankcase vent. As the exhaust gases rush out a vacuum is created in the exhaust system opening this check valve which applies negative pressure to the crankcase. You would think with 2 pistons going up and then 2 going down at the same time, pressure in the crankcase would be neutral, but it is not due to BLOWBY, which tends to try and pressurize the crankcase. This evac system sucks this out and I have found is usually good for 2 to 4 HP. Not much but if you are a supersport racer looking for a edge, it can help. This is another one of the NASCAR tricks. They actually use a pump to evacuate the crankcase. Something similar to a smog pump on a car. If anyone is interested in this I will post the NAPA part# for the valve.

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