This system drops pressure in the bottom end, the crankcase the way a
PCV system does, in fact part of the system is a PCV type setup. However
since race cars tend to run at WOT and PCVs do not work well at WOT due
to a lack of vacuum, this system adds additional low pressure at WOT by
tying into the exhaust and using the high speed exhaust gasses to pull
down the pressure in the crankcase. The system must be run with nearly
open exhaust because any significant back pressure will negate the
effects. You can run it with a nice open muffler and still get most of
the benefits, but a really quiet exhaust is not gonna work. And it must
be run with a large oil separator to keep oil from being drawn into the
exhaust. The separator is critical and must be well designed and large
enough to allow oil vapor and liquid to separate from the gases and then
be returned to the crankcase. The last one I built was for a Datsun 510
(1600cc) and I fabbed an oil separator/breather plenum that was over a
gallon in volume. It incorporated an elaborate system of baffles and oil
traps. And it had an oil return line so oil that was collected in the
separator ran back down into the case. One way valves prevent exhaust
gases from entering the intake or gas vapors from entering the exhaust,
and the oil separator prevents oil from entering both. There really is
not much risk of such a system, if well designed, dumping oil all over
the track in an engine failure, at least no more so than the basic
inherent risk of an "oil spill" in an engine failure. In fact the risk
in most cases is less because the system prevents pressure from building
in the case, and blowing oil past the seals etc..
If properly designed, the system will significantly draw down pressure
in the crankcase, and I mean significantly. And this will actually help
to prevent oil leaks. And the reduced pressure will help the rings seal
more efficiently. So all in all I wouldn't worry too much about the
system being unsafe or dangerous. I would wonder about its legality. As
far as I know SCCA does not allow it at all. And I doubt many vintage
groups will allow it unless the cars were run that way originally. I
would also wonder about the system as your mechanic is envisioning it.
Morroso and a few others sell a so-called system which is problematic
and I would not suggest. It does not incorporate a proper oil separator
and breather plenum and can lead to problems with oil spills etc. Those
sort of "systems" are for the drag race crowd, and even then it is
pretty much wannabe types that use it.
John.Desantis@inficon.com wrote:
> My engine builder is trying to talk me into using a pan evac system on my
> 66 Mustang 289.
> The pan evac uses pressure pulsations in the header to pull a vacuum on the
> valve covers.
> This sounds like a great way to deal with blow by the rings.
>
> Anyone have any experience with this? Is this common or even legal in
> vintage?
--
Marc Sayer
Journalist, Photographer, Dog Trainer (APDT member #062956)
Passions -
Great Danes, auto racing and fast cars, my wife
Dogs -
Gracie, Tank, Delilah, PJ, & the rescue dogs
Cars -
82 280ZX Turbo, 83 Volvo 245, 93 Ford E150 Tow/dog van
71 510 Trans Am vintage racer, homebuilt Formula V
My Homepage - http://gracieland.org
Deaf Dane Rescue Homepge - http://gracieland.org/DaneRescue/
Any Dane at the races is a Great Dane!
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