[Diy_efi] Venturi effect crankcase breather

[Shannen at grolen.com]

DI>----- Original Message -----
DI>From: <Shannen at grolen.com>
DI>To: <diy_efi at diy-efi.org>
DI>Sent: Friday, July 11, 2003 6:04 AM
DI>Subject: Re: [Diy_efi] Venturi effect crankcase breather


DI>>
DI>> Matt, you're right on the money here.  The Positive Crankcase
DI>> Ventilation system is designed to draw air through the crankcase
DI>> during high vacuum conditions by using engine vacuum sourced
DI>> after the throttle plates.  The PCV valve will seal as crankcase
DI>> when the crankcase pressure increases above manifold pressure,
DI>> forcing crankcase vapors out the breather tube.
DI>>
DI>Not Matt, but as you know, under NA WOT (or near) conditions
DI>the vacuum, from it's source, is no longer available, as well as, during
DI>boost conditions in FI.  With the addition of an independant vacuum source
DI>to supply a vacuum, of the strength (at the source of the vacuum) noted in
DI>earlier posts,  ring seal can/will be augmented, and as noted, without any
DI>apparent downside that I am aware of.  This is something the
DI>aftermarket/perf. industry has been aware of.

For one reason or another, negative crankcase pressure has been around
the racing "business" for many years.  Now the idea seems to be showing
up on the street.  This new market may bring positive experiences to
light or it may fuel a storm of BS like Teflon oil additives and split
electrode spark plugs.  I guess time will tell.


DI>My effort(s) were
DI>intended to show the shortcomings of the oem pcv system.  Keeping
DI>pressure out of the crankcase is important to ring (top ring) seal.

I'm not a student of ring design.  I do know that we have better designs
now than the basic square rings of the "old days."  While the old square
rings didn't have any features to take advantage of gas expansion or
pressure difference, new rings do.  It doesn't take long when playing
with a boosted car to realize that you are absolutely correct about the
importance of pressure difference across the rings.


DI>>
DI>> Look for a post in the archives titled "wicked squeel" or somesuch
DI>> to see what happens to a GM engine when a substantial vacuum is
DI>> introduced in a tpi equipped v8.
DI>>
DI>Search turned up June 10 of this year, which is unavailable in archives.
DI>:shrug:

Sorry.  My bad.  The title is "Wicked Squeaks..."
http://www.diy-efi.org/diy_efi/archive/1997-September/msg00464.html

This guy did a lot of work in the process of looking for the cause of
the problem.

Shannen

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