Arrggh--another 4k bounce. Mark, you really should up that a little.
>>
Nope, you won't get "vapor Lock" or any other issue. The only thing keeping me
from doing the same thing is some really sharp SCCA and SOVREN tech inspectors
here in the Northwest--they don't like the potential for fogging down your
competitors with a nice oil mist. The rules say "catch can".
First of all, vapor lock is a popular term that describes gasoline getting hot
enough in the fuel lines to make the fuel pump cavitate to the point it can't
pump or boiling in the float bowl that screws the carb up.
Crankcase volume changes all the time as the pistons rise and fall. Nothing
like it does on a BMW boxer motorcycle engine, but it changes. Add a check
valve (PCV) and you can pull a vacuum on the case. There's also some blowby
past the rings and a lot of off-gassing low boiling point liquids in the
oil--mostly water. All crankcase and valve cover vents do is release the
pressure. The valve cover area is open to the crankcase so it's pressurized
too and very susceptible to leaking, therefore its a good idea to vent it.
It's a long way from the valve cover to the crank vent so even if you have a
good crankcase ventilation you'll have higher pressure in the valve
cover--probably. If you get too much pressure, the seals will leak like a
sieve, especially scroll seals or felt ones. And our tractor motors have a
weak hold on their fluids under the best conditions. Drawing a slight vacuum
on the crankcase and valve cover would be a pretty good thing.
Now, if you're worried about emissions and a PCV system, then that's a whole
different ball of wax. I've never studied emission controls beyond figuring
out how to remove them from racing motors.
-----Original Message-----
From: fot-bounces+billb=bnj.com@autox.team.net on behalf of Steven Preiss
Sent: Sat 12/29/2007 5:24 PM
To: Peter Vucinic; 'Tony Drews'; 'William G Rosenbach'
Cc: fot@autox.team.net
Subject: Re: [Fot] Valve cover breather
Do you mean "...exhaust venturi scavenging positive pressure from engine
crankcase, and rocker cover venting via the vent on the catch can?"
I always thought the crank case and valve cover vents acted in tandem to
allow the engine to breathe in both directions. If a vacuum is applied to
both, wouldn't that cause a vapor lock? I also thought that the crank case
breather tube was designed to draw out the "vapor" when the vehicle was
moving, with increased vacuum at speed. I believe that when a closed system
was required by emmission control regulations, the pop-off valve was
employed to direct venting to the intake manifold when the vehicle is
stationary, and to the carbon canister when the vehicle is in motion. Please
correct me if I am wrong. (Was replacement of the carbon canister a part of
scheduled maintenance?)
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