Who's running a catch can?

modme · 06-10-2011, 07:24 AM

Quote:

Originally Posted by wstar

I posted a DIY when I did mine, over here: DIY - Oil Catch Can (w/ M370 + Batt Reloc). Mine's specific to my setup though (M370 intake manifold, and an empty battery compartment as a convenient location - may as well use the battery compartment heat shielding to promote vapor condensation in the can), but there's some general notes and ideas there too if you read through it.

All in all, doing your own catch can install is pretty simple once you understand where things hook up, you just have to decide where and how you'll mount/attach it.

I would think in general you'd be right about FI getting more blow-by, seems to make intuitive sense. But that just puts more blow-by into the crankcase, which is mostly fuel vapor. From there you're venting the crankcase through the PCV valve, and the crankcase shouldn't be at abnormal pressure, and most of the rest of the vapor is oil vapor from there. It may be that the rate of catch can condensation is mostly driven by crankcase pressure/airflow, which shouldn't vary much for FI vs NA.

Actually, crankcase pressure/airflow are completely different from NA versus FI. In NA, you will never reach positive pressure inside the intake manifold. During WOT, pressure in the manifold will drop down to zero, the PCP valve will close and crankcase air will vent minimally through the crankcase vent.

However, in FI, your manifold pressure will reach up to 12 psi or whatever boost level you are running during WOT. So now the PCV valves close, but you have significantly more pressure venting from the crankcase vent to the air intake piping. How much oil vapor is blown through during this process, I am not sure.

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.

Maila87 · 06-16-2011, 04:04 AM

Guess that experience from 350Z or any predecessor engine will help. Is catch can really so important for our cars which don't have direct fuel injection?

Carbonization is really painful on AUDI engines with FSI (Fuel Straight Injection) , or TFSI (Turbo FSI). My old 2.0T FSI with 82 000 km's on the clock didn't have any issues. But on other hand, there is owners in US which experienced problems after 1000 miles! Even RS4 are really sensitive and catch can should be factory fitted, due to liquid which looks like mud in catch can cas

BTW: Due to no big fuel quality difference and huge price mine 2nd hand TT used 95 RON fuel instead factory recommended 98 RON

wstar · 06-16-2011, 07:21 AM

Quote:

Originally Posted by Maila87

Is catch can really so important for our cars which don't have direct fuel injection?

It's just another one of those minor optimizations. I doubt it's "really important" for anyone unless you're running FI and/or a very aggressive tune that's more octane/knock-sensitive than stock.

The vapors condense to some nasty greasy stuff for us, but at the rate of 1 tbsp per 500 mi mixed into your intake air, it's not a *huge* amount. It will contribute to carbon/sludge buildup over the very long term though, and it will effectively very slightly reduce your fuel octane rating.

06-10-2011, 07:59 AM	#2 (permalink)
wstar A True Z Fanatic Join Date: Mar 2009 Location: Houston, TX Posts: 4,024 Drives: too slow Rep Power: 3596	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

06-16-2011, 04:04 AM	#3 (permalink)
Maila87 Base Member Join Date: Apr 2011 Location: Prague Age: 38 Posts: 138 Drives: 370Z Rep Power: 16	Guess that experience from 350Z or any predecessor engine will help. Is catch can really so important for our cars which don't have direct fuel injection? Carbonization is really painful on AUDI engines with FSI (Fuel Straight Injection) , or TFSI (Turbo FSI). My old 2.0T FSI with 82 000 km's on the clock didn't have any issues. But on other hand, there is owners in US which experienced problems after 1000 miles! Even RS4 are really sensitive and catch can should be factory fitted, due to liquid which looks like mud in catch can cas BTW: Due to no big fuel quality difference and huge price mine 2nd hand TT used 95 RON fuel instead factory recommended 98 RON __________________ -->2005-6 Nissan Micra 1,3i CVT 72PS Red MY 98 -->2006-8 Nissan Almera 1,5i N16 96PS Red -->2007-8 Skoda Fabia Combi 1,2HTP 3 cylinder 60PS Green -->2008-11 AUDI TT 2,0TFSI FWD S-tronic 200PS Red MY06 -->2011 Nissan 370Z manual White Pearl

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