Who's running a catch can?

wstar · 06-10-2011, 07:59 AM

Yes, that's basically true. Given positive manifold pressures from FI, I wouldn't be surprised if some of your crankcase venting ends up exiting the fresh air inlet tubes under hard acceleration as well (as you'll be building crankcase pressure from blowby, but the positive manifold pressure will keep the PCV valve forced closed). I doubt the factory puts one-way valves in them (which aren't a great idea), so you might want to experiment with canning those as well.

Another thing could affect all of this on NA cars is your driving patterns I guess. Engine braking produces more vacuum than idle or steady-state driving (faster rate of PCV system flow), whereas hard accel (WOT) produces almost no vacuum (slower rate of PCV system flow). If you use engine braking a lot, you could be scavenging from the crankcase at a higher average long term rate.

06-10-2011, 07:59 AM	#12 (permalink)
wstar A True Z Fanatic Join Date: Mar 2009 Location: Houston, TX Posts: 4,024 Drives: too slow Rep Power: 3595	Yes, that's basically true. Given positive manifold pressures from FI, I wouldn't be surprised if some of your crankcase venting ends up exiting the fresh air inlet tubes under hard acceleration as well (as you'll be building crankcase pressure from blowby, but the positive manifold pressure will keep the PCV valve forced closed). I doubt the factory puts one-way valves in them (which aren't a great idea), so you might want to experiment with canning those as well. Another thing could affect all of this on NA cars is your driving patterns I guess. Engine braking produces more vacuum than idle or steady-state driving (faster rate of PCV system flow), whereas hard accel (WOT) produces almost no vacuum (slower rate of PCV system flow). If you use engine braking a lot, you could be scavenging from the crankcase at a higher average long term rate. __________________ 7AT Track Car! Journal thread / Car setup details

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