case windage and pumping losses.. vacuum

[davidl]

Still woryinhg away at this.

Latest idea.. divide the case into three comartments.

Each will be pressurised on the downstroke of the boxer pistons.

Now all we need is a nonreturn valve on each.. will generate greta vacuum, and reduce pumping losses round case.

Oh.. and no need for scavenge oil pump...

Comments please.

David

Comments please

[Grady Clay]

David,

I’m not quite sure what you are proposing. Go look at my prior post on this subject.

I did engine dyno experiments with a smog pump pulling low pressure on the crankcase with significant results. I think the two major reasons are: less density air/oil on the back side of the piston to move around the bearing webs, crank, rods, etc. and less dense crankcase atmosphere so the oil drops out of suspension faster.

Best,
Grady

[Jim Sims]

Standard automotive air pumps (smog pumps) can't do this for long as the oil they ingest from the crankcase destroys the seals. There are modified air pumps for this type of service. Jim

[ChrisBennet]

Grady,
I did a search but I couldn't find your prior posts on the subject. Any hints on what to search for? I searched on "vacuum", "crankcase", "pumping", without success.
-Chris

[davidl]

Hello, All.

The idea is the pistons pressurise the case when they come together.. if we divide the case into three tight compartments..

This can blow the oild and air out, when the pistons rise agin, the pressure drops as there is a one way valve on the outlet of the case..

Kind regards
David

[Grady Clay]

Chris,

I found this in my file. I can’t tell if it was a Pelican post or an e-mail. It wasn’t long ago.

“Yes, in the mid ‘70s I built a vacuum system for a 911 engine on our dyno. I could get the engine sump down to about 0.4 bar using a smog pump. I think the limiting factor was we didn’t use crank seals that were bi-directional. Putting the seals in backwards worked OK with vacuum but would pump oil out otherwise.
“With the advent of larger sump pumps (’75 930 and later), better sealing P&C (Nikasil) and using a ball check valve in the vent line from the engine to the sump tank even better results were obtained.
“Of course performance gains were in the 6000 to 8000+ RPM range. Unfortunately, I didn’t do a lot of comparative testing. Perhaps others can offer 2c.”

I had several different smog pumps to use and the drive was with a variable speed electric motor. It was situated in the vent line (internally reinforced) between the top of the case and the sump tank with a filter and oil separator after the pump.

In hindsight I think air leaks at the oil return tubes and MFI seals also contributed. That is also when I realized the aneroid needed to be vented totally to the outside, duh.

I would like to go repeat these tests with today’s instrumentation.

Best,
Grady

[ChrisBennet]

Thanks Grady!
-Chirs

[Grady Clay]

I see what David is talking about. He is proposing sealing off the number 3 main web toward the #4 main on the 4-5-6 cylinder side and toward #2 main on the 1-2-3 cylinder side. That would isolate the 3&6 cylinders. With a large volume ball or flap check valve and a pick-up down low and behind the pressure pump would pump the scavenge oil to the sump tank. Of course the #3 main web would have to be extended to the bottom of the case with provisions for the oil pressure pump and drive shaft. Similar process to isolate the 2&5 and 1&4 cylinders.

These are things I thought about in the late ‘70s but never implemented. I think I would want an external pressure pump with a 3-section scavenge pump. The case pressure valves to mostly keep the internal pressure low. It would be fun to try.

Best,
Grady

[racing97]

I also in the late seventies tried a 4 stage weaver scavange pump, cam driven pulling from the individual cam towers as well as one stage from the front lower case and the rear. It did not have any significant effect on the dyno or the track. If you use a clear piece of surgical tubing as a breather hose on the dyno you will see a solid colum a foot long of oil fill the tube during your sweep. This is oil gathering around the crank causing all kinds of windage problems and HP loss, although around 7000 rpm it finally lets go and that is what you see in the breather tube. I would suggest a scraper of some sort to pull the oil off of the crank at BDC so lubrication would still occur on the cyl walls but would not ball up around the crank.