[s-cars] More Positive Crankcase Pressure 101

[QSHIPQ at aol.com]

Gary:
Thanks for the BTDT.  I suspect you have other motor issues here, but your 
points are valid.  Remember guys, the whole *reason* for CCV, and the cause of 
Positive Crankcase Pressure, is that both the block and the head are pumps 
above and below the combustion chamber.  Pumps that create pressure.  It could 
very well be that a really small vacuum line and low vacuum source isn't enough 
to completely equalize the pressure in the closed loop CCV.  If you look at the 
10vt I5 as an example, the CCV hose to the inlet side of the turbo is about 
.5in in diam.  Same for the N/A v8 stock application.  That's why Hap, I 
question the effectivenes of a tweeked motor (higher VE) to be able to use a smaller 
line of a smaller size in a closed loop CCV without a higher vacuum source.

As a rule, "smaller" vent lines are usually routed to higher vacuum sources.  
The overall theory and application being that you want the Pcc and Pvc 
(Pressure crankcase and Pressure valvecase) to equal atmospheric at all rpms, or 
Pcc=Pvc=Po.  As Gary figured out, many times other ways for that to happen, often 
will.

A catchcan vented to atmosphere can work Gary, it worked quite well on the 95 
S2 rallycar I serviced.  The vent filter needs to be serviced as Positive 
pressure is trying to force out of the filter, which can clog it pretty quickly.  
Too much vent pressue is usually an indication that the rings in the motor 
need service.  This should also manifest itself in higher oil temperatures and 
consumption due to the increased aeration.

HTH

Scott Justusson
QSHIPQ Performance Tuning


In a message dated 12/8/2003 7:48:33 PM Central Standard Time, 
gary.kaklikian at hp.com writes:
But I would avoid routing the crankcase vent to a catch can vented to the 
atmosphere without some other means of scavenging the crankcase pressure.  My 
next experiment will be to install a homemade oil filler cap with a one-way sump 
pump check valve to hopefully reduce crankcase pressure, but I'm not convinced 
this will have much effect on oil consumption.