CRankcase vacuum
 

Hello all.

Hot stuff in the V8 world..

I wonder if it will work for our little air coolers?

The case pumping losses would be greatly reduced..

Anyone done it?

David

That guy in Texas who made Doom I and II and holds a land speed record or two. Tip of my tongue...

He ran considerable vacuum in Doom I (911 motor) and II (968 motor).

-Chris

EDIT: Bob Norwood of Norwood Autocraft

On a dry sump system the tank would need to be on the low pressure circuit or it will greatly hinder the scavenge pump.

I guess the lower limits will be determined by what pressure might result in the collapse of either the tank or the flexible lines.

Might be worth a net 8 or 9 horsepower since that's the apparent gain crankshaft scuplting, piston skirt triming and web boattailing seems to achieve in a 911 engine. The converted air pumps typically used (original carbon seals have to be changed out to something more oil resistant) seem to need about 3/4 horsepower to pull a V-8 down to 15 inches of mercury. That would give one a gain of around 9 hp with probably most of the gain above 4000 rpm. In addition to the vacuum collapse issues of the oil tank and S-hose one would also need to worry about keeping enough net positive suction head (NPSH) on the oil pressure pump to ensure that cavitation of the hot oil didn't occur.

At the risk of stating the obvious..
The oil tank on a 911 is in the low pressure circuit already.
The 911 pump is two pumps in one: one pumps the oil out and into the cooling lines and eventually into the tank, the other takes if from the tank and delivers it to the oil galleries.
-Chris

I think what 350HP930 mean't was the 911 oil tank should also be at vaccum (low side) so that the scavenge pump has the same background pressure (the partial vacuum) on both sides so it doesn't have to deal with reduced suction head. The oil tank could be kept at atmospheric pressure with crankcase at partial vacuum (better for the pressure pump) but this would make the situation 350HP930 is warning about. Cheers, Jim