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Thread: PCV

  1. #1
    Senior Member DYNO OPERATOR
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    Apr 2008
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    496

    PCV

    HOW WILL I KNOW WHAT TYPE OF PCV TO USE ON MY NEW MOTOR,IS THERE SOME TYPE OF CALCULATION TO USE OR DOES IT DEPEND ON HORSEPOWER

  2. #2
    Senior Member DYNO OPERATOR
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    Apr 2008
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    Are you asking about a Positive Crankcase Vent? If so, that is an emission device basicly. If you have a racing engine that this question pretains to, don't use it. It will bring oily air in to the intake and probably will build up on the intake valve back side that WILL hurt air flow. Stock engines have short run intervals and require this vent to remove condensate and fuel vapor from the oil in the crankcase to prolong its life. Race engines change oil often and don't like air leaks below the carb that the factory makes as part of there intake air. I hope this helps you with your question. If you are a stock engine basicly I prefer one with a heavy spring and a small opening to limit the velosity of the incoming air leak from the oily chamber below.

  3. #3
    Senior Member DYNO OPERATOR
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    THE CAR WILL JUST DRAG RACE.SHOULD I USE HEADER EVACUATION OR JUST PUT BREATHERS ON THE VALVE COVERS OR DO NOTHING AT ALL?

  4. #4
    Senior Member DYNO OPERATOR
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    Any thing that puts the crankcase in a low vacume condition is king for ring seal reguardless of ring package. I would at the minimum, use a headder vent to each collector with the check valves at the exhaust nipple. NEVER go without a vent. try to get both valve covers sealed up and one scavenger vent per side per collector is the least expensive way I know of to do this. Other wise a vacume pump possibly electric for small engines or mechanical for larger racing engines is worth power in any engine. How much just depends. I hope this helps.

  5. #5
    Senior Member RACING JUNKIE
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    Nov 2005
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    Staunton, IL
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    We had a problem with my altered. We put on a pcv system. We'll see if it helps. I already had the lines from the valve covers to the headers. My headers are too big for my combo (thye came with the car). So I wasn't getting the exhaust pulse for them to work properly. So I could've upped the compression, bought new headers, or bought a vacuum pump. All expensive alternatives.Instead we're going to try the pcv.

  6. #6
    Senior Member DYNO OPERATOR
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    A PCV system will not put your crankcase under a negative pressure condition that I mentioned previous and help ring seal under racing conditions. An open vent to atmosphere would be an improvement over a pcv in a racing engine. You decide which applies to your engine. A PCV is not active at WOT, no vac to remove crankcase pressure from W.O.T. ring leakage. An open 3/8" tube to a crankcase is not an alternative for scavenger vents that are usually 5/8" per side to keep up with the venting need at WOT. Maybe Slowmotion could elaborate what they are attempting to fix by adding a PCV to his engine it may be interesting?

  7. #7
    Senior Member RACING JUNKIE
    Join Date
    Nov 2005
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    Staunton, IL
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    943
    Engine seems to be building pressure. I'm no mecahnic but my brother is by trade. He thinks the rings might not be proprly seated yet. The engine only has a handful of passes. Like I said Just something we're going to try. A vacuum pump would be the correct fix and free up some horses but i don't have the extra cash for that right now. I need a bigger radiator and gears before that.


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