> As engines wore, the amount of blow by collected in
the crankcase increased.
> Thus causing some polution. In the mid 70s the EPA
started to require
> manufactures to reduce the total pollution of the
car.
=====
'61 in Ca. for PCV, federally adopted in '65. They
were originally plumbed to the intake.
=====
>
> However, the idea was to NOT vent this to the
atmosphere. So the routed
> it back to the intake of the carburator. Thus
allowing these excess vapors
> to be burned.
=====
Not the inlet, but at the base of the carburator
after the throttle(s) or straight into the intake
manifold.
=====
>
> I don't know when the actual PVC valve was added,
and I'm not quite sure
> of its operation. Basically all it the PCV valve
is, is a BB that is
> allowed to float in a verticle tube.
=====
It's a one way poppet valve, with a small restiction,
allowing flow only from the crankcase back to the
cylinders to be burned.
=====
When there is no pressure, the
> gases are kept in the engine. As a function of
either, or both, increased
> crankcase pressure and vaccumn, the BB is allowed
to lift off its seat
> and the gases are allowed into the carb. Same as
above.
=====
There is always positive flow. At periods of high
vacuum, such as at idle or overrun, flow is limited
to the restriction, or from the fresh air pipe to the
air filter. As manifold vaccuum drops, the spring in
the valve overcomes the reduced manifold pressure,
allowing increased PCV flow with increasing RPM.
=====
>
> As to your questions:
> "What is the difference in function? Which
should go where or
> would it be best to have 2 PCVs?"
>
> I don't know. However, my mind, one tube should be
more than enough to
> handle the excess vapors unless you have a very
worn eng. and a very high
> compression ratio. But here is where I'll defer to
the more learned
> members of our group. Anybody?
=====
You must have a circular flow pattern, whether it's a
fresh air pipe from the air filter to the one valve
cover/PCV valve from the other, or a PCV valve in
each valve cover 'Teed' to a commom pipe to the
intake or carburator base.
Two PCV valves has no inherent advantage over one,
but is less maintenance, so it's my preference.
As a biker, I was sure glad to see the demise of
those down pipes. The roads had a permanent oil slick
down the center and around the curves making for very
cautious riding. Not to mention sitting in rush hour
traffic on a hot summer day breathing all those
noxious fumes.
GM
>
> John
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