Catch-can vs. Oil Separator vs. Atmos Vent

[Spenny_b]

Originally Posted by 993Speedster

Finishing up the very last bits of the turbo build and it's time to sort the PCV/crankcase vent setup so I'm not pumping boost into case and brake booster. As I see it, I've got 3 options (with the stock setup not being one; at least in its current configuration):

1.) Catch can introduced into crankcase vent tube and catch can outlet routed to turbocharger compressor inlet.

Pro's of this setup include: cheap, easy and readily available, largely keeps oil out of intake tract
Con's of this setup: tank has to be periodically emptied depending on tank size and blow-by amount, also even though oil is separated you're introducing "dead/oxygen-less" air into the intact tract + some grime. Blow-by gasses are hot also

2.) Oil Separator (looking at Mann & Hummel ProVent 200 as everyone raves about them) put in same location as catch can.

Pro's: Still readily available, keeps oil out of intake, doesn't have to be emptied and less loss of oil level in the sump as time goes by
Con's: More expensive than a usual catch-can and requires filter media replacements every so often, still introduces hot, oxygen-less blow by into the intake taking up space of precious cold-dense intake charge.

3.) Crank vent to atmosphere (w/ or w/o a tank to catch vapors)

Pro's: cheap, easy, keeps the turbocharger and intake tract the cleanest, ensures only fresh oxygen-rich cold air is going into turbo. From what I've been told, 3-5% alteration to tune for MAF based cars that switch to vent instead of re-circulation... so it's a sizeable increase in fresh air flow
Con's: very obviously not emissions compliant but the car doesn't have a cat anyways sooooo.....


I'm leaning towards 3 because.... well because racecar?


I'd love to hear all your thoughts and what you're personally running and why...

I'm re-working my breather setup "as we speak"...I originally went to a lot of trouble fabricating an oil/air separator tank which mounts by the rear RH corner of the intercooler. Bearing in mind that mine's a 964T rather than 930; I believe the breather setup is different but I couldn't tell you how. The dry sump tank breather outlet feeds into the top of my separator, which internally has a tube to the bottom of the tank. Vapour then has to travel upwards through a couple of horizontally opposed baffle plates, then through a filter (actually a piece of a K&N panel filter, unfolded), then out through an exit pipe. This was then fed into the "snorkel" of my intake setup, after the filter (a foam ITG filter, so obviously can't feed into it). All hoses were approx 22mm I.D....loads of pics of this fabrication in my thread, linked below...

What I was attempting to do was mimic the factory method, where the breather is fed into the 964 air box, pre-filter, in hindsight presumably only for emissions, and as they weren't running massive boost or advance, it probably worked well enough. It kept things very neat, and after multiple checks while breaking in the engine, there was no oil in the bottom of my separator tank (it also has a drain plug).

However....when we dyno'd the engine a few weeks ago, we were severely limited to the amount of ignition advance we could dial in. It's suspected that this "dirty" air being fed from oil tank into the inlet tract was the culprit, massively reducing the effective octane level of the intake. We also noted that the amount of fuel compensation required at idle after a dyno run was massive, quite possibly due to the intake temp being artificially increased with this now very hot, breathed air from the tank.

Not yet checked if my changes have made a difference, I suspect we'll only know the full answer once we go back on the dyno, and dial in more ignition (or attempt to!)

So...I wouldn't do option 1 or 2, lol.

[Uwon]

Originally Posted by Spenny_b

However....when we dyno'd the engine a few weeks ago, we were severely limited to the amount of ignition advance we could dial in. It's suspected that this "dirty" air being fed from oil tank into the inlet tract was the culprit, massively reducing the effective octane level of the intake.

So... how much oil did you burn in the dyno? I suspect that you have other issues.
Johan

[Spenny_b]

Originally Posted by Uwon

So... how much oil did you burn in the dyno? I suspect that you have other issues.
Johan

How did you come to that conclusion?

No (discernable) oil burnt, and leakdowns were all less than 2%

[boosted79]

Spenny - I also doubt that is your problem. If you were running MAF instead of speed-density and the vapor return from the can was upstream of the MAF sensor I could see where it would have an effect. Since your leakdowns were so low the vapor return from the can should be very low, I don't see it causing the extent of the problem you are seeing. A comp. check and leakdown is where to start. If they check out ok then I would have a real close look at the sequential fuel and ignition setup.

[Uwon]

Originally Posted by Spenny_b

How did you come to that conclusion?

No (discernable) oil burnt,

Bad choice of words. Should have asked if you used any oil when you dyno’d that could be attributed to the vapor isssue. My thought is that you would have to produced allot, and I mean allot of oil vapor to affect performance, hence use of oil.
Johan

[patkeefe]

Uwon, thanks for the info. That is just about factory size, I think.

I am going to put a tee in my line between the breather and can so I can measure the pressure with a gauge.

[Spenny_b]

Originally Posted by boosted79

Spenny - I also doubt that is your problem. If you were running MAF instead of speed-density and the vapor return from the can was upstream of the MAF sensor I could see where it would have an effect. Since your leakdowns were so low the vapor return from the can should be very low, I don't see it causing the extent of the problem you are seeing. A comp. check and leakdown is where to start. If they check out ok then I would have a real close look at the sequential fuel and ignition setup.

boosted, I'm conscious that this sub-conversation is hijacking the OP'ers thread, but I am intrigued but not understanding your thoughts I've bolded above. To save a hijack, could you explain further your thoughts on this but over on my build thread in the Engine forum please? Thanks, S

[krasuskyp]

Originally Posted by OldSpool87

Friends don’t let friends vent to atmospere.

lolz ^^^this allllllll daaaaaay^^^