Gordon Glasgow wrote:
>
> Mine's a K&N but I don't know the part number. It's been on there for years.
>Not really a good idea,
> BTW. It's good to have some vacuum to vent the cam cover. I only did mine
>because the aftermarket
> air cleaners didn't have a fitting for the hose.
Gordon is right on about this. If your car wasn't originally designed
for venting the crankcase to atmosphere (i.e. it vented to the air
filter, a pcv system or some other low pressure or vacuum location) then
you really can't just stick a filter on the valve cover and call it
good. The reason is that the vent area will not be sufficient to prevent
pressure buildup in the crankcase without the vacuum. You need much more
vent area when venting to atmospheric pressure than you do when venting
to vacuum. This can sound a bit like nit picking but think about this,
the Evacupan system has been outlawed by most racing bodies as a
performance enhancement system. What does it do? It creates a full-time
vacuum in the crankcase. That's all. But by doing that the rings seal
better and the engine creates more power. Pressure below the rings is
BAD, anything that allows blow-by to pressurize the crankcase (i.e.
below the rings) is bad. If you want to just vent to atmosphere, make
sure you have so much total vent area that there is no way pressure can
build up (a good rule is the combined vent area should equal the
diameter of one piston) and make sure every vent has an oil trap, and
either proper filtration or a one way valve.
For those of you who have to know, the Evacupan system creates a vacuum
in the crankcase anytime the engine is running by connecting the
crankcase to the intake manifold and the exhaust. It uses one way valves
to ensure flow can not reverse, and an oil separator to prevent oil from
being drawn out of the crankcase and into the intake or exhaust. At part
throttle, when the intake manifold has vacuum, this source draws a
vacuum in the crankcase (like a pcv system will only the vacuum signal
is stronger so the pressure drop in the crankcase is higher). At full
throttle, when there is no vaccum signal in the intake manifold, the
exhaust gas speed rises and via the venturi effect, this draws down the
pressure in the crankcase. So you have a pressure drop applied to the
crankcase anytime the engine is running. Obviously this only works with
a low pressure exhaust (generally only an open exhaust will work though
I did build a system for a 510 race car once which used a big Flowmaster
muffler and the exhaust pressure was still low enough for the Evacupan
system to work) and this means race cars only. Also the positioning of
the connection to the exhaust is critical too as it must feed into the
exhaust after the final collector and facing downstream so the flow of
the exhaust gases in the exhaust pipe will draw down pressure in the
Evacupan system.
--
Marc Sayer
Editor/Publisher
Z Car & Classic Datsun Magazine
http://zcarmag.com
Voice 541-726-6001
Fax 541-746-0863/726-6001
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