[s-cars] RE: PCV - Long

Wed Feb 23 18:57:10 EST 2005

Who has a 2 1/2 " pipe, mine is 4" dia.

Lets get real here, if we generate enough vacuum in that pipe to actually do 
any good with moving oil laden air then I must submit we are losing 
potential HP by,
- increasing the PR across the turbo,
- increasing the inlet air temp because of this increased PR and decreased 
efficiency.
- having shit dirt air and less room for nice oxygen laden combustible air 
(as Trevor pointed out is his very clever post , hats off to you).

Does it make sense, why I DON'T want a negative pressure there ?

Mark
----- Original Message ----- 
From: <QSHIPQ at aol.com>
To: ""Trevor Frank"" <tfrank at symyx.com>; <Djdawson2 at aol.com>; 
<t44tqtro at gmail.com>; <s-car-list at audifans.com>
Sent: Wednesday, February 23, 2005 5:11 PM
Subject: [s-cars] RE: PCV - Long

> 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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