[s-cars] RE: PCV - Long

[QSHIPQ at aol.com]

In a message dated 2/23/2005 6:59:06 PM Eastern Standard Time, "Mark Strangways" <strangconst at rogers.com> writes:

>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
The goal makes sense, I just don't buy no vacuum in a 4in pipe.  Did one of those mods to a 034efi car, and with the addition of a bypass valve (as pcv) there was certainly not a problem with recirc.  I'm still a bit confused how one can have 600cfm flowing thru any size pipe without negative pressure.  Logic would tell me you don't have positive pressure, logic would tell me you don't have zero pressure, logic would tell me you might have 'less' negative pressure than a 2.5in pipe, but you must have some.  You certainly don't need much to pull CV, since we are speaking of oil vapors here.  In fact, the reason you run restrictors in even N/A cars, is the vacuum required for PCV is much less than manifold vacuum.

I'd be real interested to see actual numbers here wrt comparative negative pressures.  One can certainly argue that the closer you get to the turbo inlet, the higher the negative pressure.  Unless you have a 4in turbo compressor inlet.

SJ