[s-cars] RE: PCV - Long

[QSHIPQ at aol.com]

I'd be somewhere inbetween.  After taking a gander under the hood of said machine, I don't at all believe that Mr. Dawson (mr "pvc" - tm?) is anywhere close to a stock motor.  I also believe that those operating modified miss piggy at altitude are going to find turbo oil boundary blowby more common than those at atmosphere.  That's usually because turbo oil restrictors are really sensitive to oil pressure and the boundary pressures in the seals must fall into a range, or they spew black smoke.  It's a bit of a dance between restrictor size and oil pressure (+/- viscosity) and atmospheric pressure.  BTDT years ago when I thought more oil on the bearings was a good thing (the folks driving behind me never thought so).  

WRT crankcase ventilation (Dave, henceforth I'll refer to this as PCV;), my experience has been that a hold tank that returns to the crankcase has the best compromise between atmospheric and pure intake vacuum.  Atmospheric tends to stink up the ride to a good dinner (usually accompianied by a comment from the right seat "so this is *fixed*?"), and intake vacuum outright does nothing good for combustion (race engineers speak of explosions as apposed to combustion = not good).

Trevor's post reflects my thinking, keep the oil out of the intake manifold at almost all costs.  One must offset that with a reminder that all costs can sometimes be a bit on the smokey side.  30years ago, I remember adding a nozzle to the exhaust, and several of the chebby boys still do.  The problem with this thinking in todays lambda world is that O2 sensors and especially Cats, don't like to be choking on fully aerated/saturated oil byproducts.

A simple vacuum checkvalve ala pcv (of which S cars already have a pcv - ever replaced yours?) to a low vacuum source (turbo>MAF pipe) that is routed to a collector that dummps back to sump is probably the best compromise (btw, the group A S2 used this setup.  Several setups, including chrome are available from your local speedshop, btdt.  As a side note, I'm not sure how you can flow 600cfm thru a 2.5in pipe between the MAF>turbo and not have negative pressure in it Mark, but measuring it could be a problem I suppose.

I know the Haney esq motor pretty intimately as well, and I know that he kept oil from his intake.  I'd certainly venture to propose that even with a stage 1 chipset, one has enough cause for concern wrt crankcase ventilation.  One needs to think in terms engine Volumetric Efficiency of a 2.226L engine using a wet oil pcv, which means torque and/or HP is significant (stage 1 75lb/ft of torque massively increases VE).  At expected high VE, one would desire to have the least amount of oil residue in the system.  Unfortunately too, a pcv valve is switched immediately to boost input, but the oil residue isn't.

This is the first time I've seen discussion on PCV here.  I certainly believe it's quite worthy of further discussion, and acceptable compromises to atmosphere/exhaust dumping and vacuum sources can be found.  I've even found that the standard issue bosch bypass valve can be used in this PCV valve capacity with great success.

Good discussion...  Nerd on boys.

HTH

Scott Justusson
QSHIPQ Performance Tuning








In a message dated 2/23/2005 4:35:15 PM Eastern Standard Time, "Trevor Frank" <tfrank at symyx.com> writes:

>
>I will agree with Dave here, I am being hyper critical here.  Basically
>I am only talking to high hp cars that are very prone to detonation
>already as well as ones that have heavy track use with modified
>suspension and big tires.   I don't know if I can say that I have seen
>any "stock" cars having this problem "oil in the intake" turn
>catastrophic.
>
>
>
>
>-----Original Message-----
>From: Djdawson2 at aol.com [mailto:Djdawson2 at aol.com]
>
>Sent: Wednesday, February 23, 2005 12:40 PM
>To: Trevor Frank; t44tqtro at gmail.com; s-car-list at audifans.com
>Subject: Re: [s-cars] Crank Case Pressure and Turbo Smoke?
>
>
>
>
>In a message dated 2/23/2005 1:33:03 PM Mountain Standard Time,
>tfrank at symyx.com writes:
>
>
>
>
>Sorry, but I will have to disagree here, there are lots of reasons not
>to vent into the motor, so there are lot's of reasons to vent some other
>way..either to atmosphere or into a vacuum pump or into the exhaust.
>For me the issue was always about keeping blow by gasses and more
>importantly oil out of the intake track, I have seen to many failures of
>a motor due to oil in the intake.
>
>
>
>I agree with the many downsides of venting to the intake that you've
>pointed out.  However, being realistic, I think it is important to note
>that we're talking about engines that typically exceed 250K miles of
>normal life, if maintained properly.  With that in mind, I'm not really
>sure I would buy in to venting elsewhere as a critical priority.  I've
>been running my recent rebuild for about 10k miles now, and the hose
>leading to the MAF/turbo hose remains dry.  I think that normal wear and
>tear will take it's toll on the engine long before the adverse effects
>of crankcase ventilation.
>
>Anyway... I do appreciate the good points you've made.
>Take Care,
>Dave in CO
>
>
>
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