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

[Djdawson2 at aol.com]

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