In a message dated 4/10/06 9:31:23 AM Eastern Daylight Time, hoyt@cavtel.net
writes:
<< Negative crankcase pressure is used in high horsepower engines to help, I
believe, reduce windage HP losses. A separate vacuum pump is used.>>
That and lower tension piston rings can be used reducing friction. Piston
rings are dynamic devices, pressure gets behind the ring forcing it outwards
for
a better seal. This all works better if you have a slight vacuum in the
crankcase. At high vacuum levels the wrist pins can be starved for oil since
the
oil cloud is reduced.
http://speedtalk.com/forum/viewtopic.php?t=219&highlight=cross
http://www.dragstuff.com/techarticles/vacuum-pumps.html
<< At 500+ HP, I suspect that the energy used to drive the pump is negligible
versus the benefit it provides, but at our 100 HP level, it would be just
for
show. >>
The vac pump is similar to a emission air pump, HP use is in the 1 to 2
range. All size motors can benefit if ring tension is reduced, just hanging on
a
pump won't do anything other than reduce oil leaks.
Drag racers had long used a emission check valve plumbed into the exhaust and
the other end attached to the valve covers, no special venturi needed.
Harold
=== This list supported in part by The Vintage Triumph Register
=== http://www.vtr.org
|