pcv or evacuation system for a weber set up

[CompClassics]

An old drag racers trick is to apply a slight vacuum to the crankcase by installing EGR valves, one way check valves, into the collector area of the header on each side and attach a hose between them and a fitting on each valve cover or a crankcase breather. The Exhaust pulses create a suction which in turn cause a slight vacuum within the crankcase, drag racers looked at it as free horsepower as the pistons were having to pressurize the crankcase when heading to BDC.

[Gaz64]

Originally Posted by CompClassics

An old drag racers trick is to apply a slight vacuum to the crankcase by installing EGR valves, one way check valves, into the collector area of the header on each side and attach a hose between them and a fitting on each valve cover or a crankcase breather. The Exhaust pulses create a suction which in turn cause a slight vacuum within the crankcase, drag racers looked at it as free horsepower as the pistons were having to pressurize the crankcase when heading to BDC.

At any moment in time, any pistons heading towards BDC (4 in a V8) are cancelled by the same number of pistons towards TDC.

Blowby gases, combustion chamber pressure lost past the piston rings, is the cause of crankcase pressure.

Applying a low pressure to evacuate the crankcase, and if possible creating a negative pressure within the crankcase helps the rings seal better, since ring flutter will be minimised.

Hence the dragracer power increase.
Many guys run vacuum pumps these days, with a regulated vacuum, about 5 in Hg.

For my cars, I run a PCV plumbed to a hidden log where each runner gets a shared source from.
The fresh air side inlet which becomes the breather outlet under load goes to a Moroso air oil separator (self drains to the valve cover via 6an) 12an hose breather hose, then comes back to my airbox.
Not a skerrick of oil in the airbox/hose entry.

Gary

[big deuce]

Originally Posted by CompClassics

An old drag racers trick is to apply a slight vacuum to the crankcase by installing EGR valves, one way check valves, into the collector area of the header on each side and attach a hose between them and a fitting on each valve cover or a crankcase breather. The Exhaust pulses create a suction which in turn cause a slight vacuum within the crankcase, drag racers looked at it as free horsepower as the pistons were having to pressurize the crankcase when heading to BDC.

Very true, and way more effective on larger cubic inch engines. Dad and I built an off topic 505 bbc for our drag car and used that exact setup; until we had it dyno'd. The machine shop said, " lets put a evac pump on the crankcase", threw a moroso evac pump on and hp went from 790 to 820hp with no other changes. Oil pressure was rock solid also, not so much without the evac.