Quote:
Originally Posted by gmsii
i am guessing people want to extol the benefits of crankcase gas recirculation based almost solely on the last sentence. conceptually it is correct...pulling vacuum in the crank case has an effect on sealing the rings.
but... who can answer how much vacuum needs to be pulled for it to matter? if you can answer that, then you will know the pcv system does little to seal rings. funny enough, the pcv wont do squat for sealing rings when the engine needs it the most at WOT because the manifold vacuum is near zero.
from a practical standpoint, the amount of vacuum needed in the crankcase to make a difference is MUCH higher than what you might think, and it certainly cannot be passively pulled by the intake manifold passively pulling through a tiny rubber PCV tube. on race engines we need to use multiple -10 or -12 lines and a stout pump to actively pull enough vacuum for it to matter in terms generating more power from better ring seal. and im talking using standard tension rings. if you use low tension rings, you need to be pulling even more vacuum.
anyways PCV recirc is for emissions and not performance
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I'm not saying you're wrong, I'd just like to challenge that in a race application there will be much higher flow past the rings/into the crankcase, due to the higher average cylinder pressure compared to that of a daily driver at cruising loads. This higher flow would require more flow out via the vacuum pump to make the same difference.
I'd love to actually get my hands on something that shows the engine load vs pcv air flow vs crankcase pressure. I know it would vary from platform to platform but even a general idea would be helpful.