PCV - Help or Hurt?
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From: Fowlerville, Michigan
PCV - Help or Hurt?
Does the PCV system help or hurt performance? I read an old Hot Rod Engines magazine that claimed it's a neutral deal - it doesn't take from or add to performance. Just pulls the vapors out of the crank case back into the induction system. I question the article though because it was written in '85 when emissions stuff was "the thang".
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Here is an explanation, so you under stand, not just taking my word on it.
When you pistons travel up and down, yes it build compression in the cylinder. but also builds pressure going down in the crank case. If you plug the pcv system, it will hurt performance, and it will cause seal failure. In racing engine aplication, most guys will hook a hose between the valve covers, and the collector. This causes suction. Some engine builders use a vacume pump. Idealy when trying to make HP and TQ you want to use power wisely, so a neg 3 psi vacuum in the crank case is perferred.
Oldsmobile used an electric vacuum pump in the 90's I have seeen guys hook them up to 1 valve cover, and put a pit **** and presure guage on the other. turn the pump on, and open or close the valve to acheive -3 psi on the guage.
I hope this helps you understand, not only does the pcv system releive pressure, it also carry's away condensation, as the oil heats up.
When you pistons travel up and down, yes it build compression in the cylinder. but also builds pressure going down in the crank case. If you plug the pcv system, it will hurt performance, and it will cause seal failure. In racing engine aplication, most guys will hook a hose between the valve covers, and the collector. This causes suction. Some engine builders use a vacume pump. Idealy when trying to make HP and TQ you want to use power wisely, so a neg 3 psi vacuum in the crank case is perferred.
Oldsmobile used an electric vacuum pump in the 90's I have seeen guys hook them up to 1 valve cover, and put a pit **** and presure guage on the other. turn the pump on, and open or close the valve to acheive -3 psi on the guage.
I hope this helps you understand, not only does the pcv system releive pressure, it also carry's away condensation, as the oil heats up.
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Senior User
Joined: Dec 2008
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From: Fowlerville, Michigan
Very good explanation. I have heard that crankcase vacuum promotes piston ring seal. What I want to know now is, if 3" of vacuum is preferred in the crankcase, how is that achieved when you have a breather? The intake vacuum pulls through the PCV valve but the breather lets air into the system so there's really not much vacuum in the crankcase. Couldn't more vacuum be achieved if you yanked out your breather and capped the hole?
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