Another way to reduce pumping losses

[300zxrb26dett]

Its one of those things that you could do if you had an engine already apart to rebuild. While I am sure it would be "splitting hairs" but if you split enough hairs you can get one whole hair, right?

[3-Wheeler]

Originally Posted by oil pan 4

A high vacuum would be bad. Having about -5psi or 10''Hg is ideal....

You would have to ensure that the rubber crankshaft seals and such would actually withstand such a high differential pressure, between the vacuum in the crankcase and the outside world.

I doubt that normal lipped rubber crankshaft seals would withstand such high vacuum.

More modern seals have very low lip strength, to allow less rotating friction, and would only handle about 1 inchHg vacuum before the seal starts to fail because of the thinness of the rubber.

Jim.

[mwebb]

on VW and BMW
it is not uncommon to have a crankcase vent valve fail
one of the failure patterns vents intake vacuum to crankcase
when that happens
the seals sometimes , but not always
whistle

the seals are usually not damaged and hold the oil where it belongs after the repair

[Ken Fry]

Originally Posted by bandit86

By increasing the vacuum in the crank case you can do the same.

I think these are actually slightly different effects. The notches permit air to more easily flow from under the pistons going down (for example 2 and 3) to under the pistons going up (1 and 4).

Pulling a vacuum in the crankase acts equally on the pistons going up (impeding their motion) and those going down (helping their motion). The lowering of pressure overall reduces air density, which reduces windage.

So one effect is permitting easier cylinder-to-cylinder flow, and the other is reducing the drag effects of air.

This is splitting hairs, of course.

[bandit86]

Originally Posted by oil pan 4

A high vacuum would be bad. Having about -5psi or 10''Hg is ideal.
Word on the street is a high vacuum pulls oil away from wrist pins. It would also cavitate the oil pump, before pressurized hydraulic oil tanks came along aircraft above 30,000ft could have their hydraulic pumps cavitate do to lack of absolute pressure on the return side.
You might be able to go as high as 15''Hg to 20''Hg on a non racing application. Monkeying with your oiling system is playing with fire, I took a risk by running low tention oil rings on my diesel and it seems my reasoning for needing standard or high tension oil rings was sound. (diesels dont need them because they don't draw much vacuum)

I don't see how vacuum in the oil tank would cause cavitation. Oil pumps turn at a surprisingly low speed, I watched a giant v8 diesel from a semi with the valve cover removed and the oil trickled from the valve area at best. The rest of the system relies on pressure, and will not splash much oil.

[EdKiefer]

This might have advantage with motorcycle engines (compact size) but on car engines its not a problem . With older type that use a saddle caps for main bearings there is plenty of room for air to circulate around, oil pans are larger than level .
With newer , aluminum block that use girdle type main bearing bolting, many do have vent whole right below cylinder bores for air to move around .

Also in general the motorcycle rev's a lot high than a car engine so more whipping of air .