[Diy_efi] Venturi effect crankcase breather

[arnie]

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


>
> Matt, you're right on the money here.  The Positive Crankcase
> Ventilation system is designed to draw air through the crankcase
> during high vacuum conditions by using engine vacuum sourced
> after the throttle plates.  The PCV valve will seal as crankcase
> when the crankcase pressure increases above manifold pressure,
> forcing crankcase vapors out the breather tube.
>
Not Matt, but as you know, under NA WOT (or near) conditions
the vacuum, from it's source, is no longer available, as well as, during
boost conditions in FI.  With the addition of an independant vacuum source
to supply a vacuum, of the strength (at the source of the vacuum) noted in
earlier posts,  ring seal can/will be augmented, and as noted, without any
apparent downside that I am aware of.  This is something the
aftermarket/perf. industry has been aware of.  It's still refreshing
to read posts from those that don't play word games.  :)
>
> The breather tube is generally connected on the atmosphere side
> of the throttle plate.  The fact that crankcase "waste" vapors are
> drawn into the manifold rather than released to atmosphere is what
> caused many mechanics and pundits to fear reduced engine life
> when the PCV system was introduced in the 60's.
>
> The total vacuum in the crankcase is system dependent, however.
> Many stock GM vehicles show little to no vacuum as the breather
> side of the PCV system offers little restriction to fresh air.
>
If my posts inferred the crankcase was able to maintain a vacuum
when exposed to such by the induction system, that was unintentional.
Obviously, with fresh air being drawn in on one side, via breather or tube
to TB, this would be very difficult to achieve.  My effort(s) were
intended to show the shortcomings of the oem pcv system.  Keeping
pressure out of the crankcase is important to ring (top ring) seal.
>
> Look for a post in the archives titled "wicked squeel" or somesuch
> to see what happens to a GM engine when a substantial vacuum is
> introduced in a tpi equipped v8.
>
Search turned up June 10 of this year, which is unavailable in archives.
:shrug:
>
> Shannen



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