[s-cars] Crank Case Pressure and Turbo Smoke?

[Mark Strangways]

Too add,

The opposite may be true as well, during a flow (boost) conditions there may 
be enough restriction in the MAF to turbo hose and MAF to allow a suction to 
develop in that hose, this would certainly cause oil fumes to be excessively 
drawn into the intake system.

Which way is that pipe (off the valve cover to the MAF-Turbo hose) designed 
to flow.
It should pull air out of the clean intake stream or is it designed to just 
vent gases to the intake stream.

Mark
----- Original Message ----- 
From: <Djdawson2 at aol.com>
To: <cpayne at bconnected.com>; <s-car-list at audifans.com>
Sent: Tuesday, February 22, 2005 1:02 AM
Subject: Re: [s-cars] Crank Case Pressure and Turbo Smoke?


> In a message dated 2/21/2005 5:16:55 PM Mountain Standard Time,
> cpayne at bconnected.com writes:
>
>> Suggestion; if you have not already made significant upgrade to you
>> crankcase breathing system, do so."
>>
>> This is really something I dont understand too well...nor know how to
>> alleviate or measure to see if that is the cause
>>
>
> Cody,
> The possibility of excessive crankcase pressure sounds feasible to me.  On
> the higher capacity compressors, I have noticed that when bypass occurs,
> crankcase pressure can become positive.  The crankcase breather 
> essentially runs from
> the crankcase to the back of your valve cover, and then from the valve 
> cover
> to the "MAF to turbo" hose.  Your valve cover is not vented, it is really 
> just
> a tube through the valve cover that has no flow to the valve/cam area 
> itself.
>
> When your engine is under load (producing significant boost), and you let 
> off
> the throttle... the bypass valve opens.  When the bypass valve opens, a
> significant amount of pressure is "bypassed" back into the MAF to turbo 
> hose.  This
> also happens to be where the crankcase ventilation also resides.  I 
> believe
> that the sudden pressure in this hose causes a pressure flow back into the
> crankcase.  This will definitely cause smoke.
>
> You can very easily (and cheaply) test my theory.  Go to any decent auto
> parts store and look through their selection of PCV valves.  Find one with 
> an OD
> that is the same as the ID of the hose that goes from your valve cover to 
> your
> MAF/turbo hose.  These are usually under $5.  Also get 2 hose clamps.
>
> Cut the valve cover vent hose, and install and clamp in the PCV valve. 
> The
> PCV valve is really just a one way check valve.  Make sure you install it 
> such
> that the valve closes any time pressure is moving in the direction of the
> valve cover.
>
> I think this may solve your problem.
> HTH,
> Dave
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