Do I need a PCV valve or are 2 breather caps OK? Is there any advantage of one or the other? This is on a new 347 stroker motor. Currently it has 2 breather caps, came with one from the builder and I just bought another one.

Chris

 

Everyengine should have a functioning PCV system. The purpose of the PCV system is to ventilate nasty crankcase gases back into the intake to be burned and dumped out the exhaust. Without an active pcv, all of thoses gases sit in the crankcase and build up a nice gunky, corrosive residue on everything. If the base of your carb doesn't have a large vacuum hose fitting, you can get spacers that have a threaded fitting for one.

 

I concur. While two breather caps would provide crankcase ventilation (CV), it's not adequate as it relies on atmospheric ventilation, which in the case of a V8 engine is relatively non-existant. The PCV valve when routed tomanifold vacuum creates the "positive" aspect of the ventilation process by forcefully "sucking" the gases out of the engine and burning them up.

Dave

 

Plus it looks bad when you are showing your buddies your engine running and the blowby gasses are puffing out the breather. Every engine has a little blowby and its got to go somewhere.

 

Or out of the dipstick hole..

 

In addition to what the other guys said, if there is any positive pressure in the motor it will encourage oil leaks.

 

ok i have a question,...

i am about to fire up a 302, i have two breather caps also, edelbrock ones, doesnt make a diff, but anyway,...

i have two other cars where the crankcase is vented to a catch can, cause i was told that running this dirty oily air back into the air system is bad,...having oil in the air track actually lowers the octane of the fuel which causes less power

now both of the other cars are highly modded turbo cars, but i dont think that would make a difference,..i was told you want that air out of the engine and out of the intake,...

cause i was thinking of running different caps with outlets to a catch can,...

 

How much power do you think you lose to the fact that the pistons need to shove all that "air" around inside the crank case ? With the P.V.C. you are actually creating negative pressure inside the block. This actually Up's horsepower gains.

 

If you have alot of blow by the oil will end up fouling the plugs. Otherwise in a well functioning engine you would not notice the HP loss due to PCV.

 

Wouldn't the breather caps also allow that "air" to escape, without compressing? I hadn't considered the "negative pressure" aspect before.