Wet sump external oil pump

[Travis Horton]

How many inches of vacuum would you expect to see on a bbc with a full length pan? Would higher oil pressure affect the vacuum, if any?

[KnightEngines]

With a single stage external pump - 0psi.
A single stage is just not big enough to pull a vac, if you want vac with a single stage pump you're gonna need a vac pump.

[Travis Horton]

That's what I figured. A friend had a 598 on the dyno and was concerned that it was showing less than one inch of vacuum. Thanks!

[roc]

Crankcase pressure (vacuum) wise, I don't know why a single-stage external pump would be any different than an internal pump.

[andyf]

A 598 inch engine is going to require a serious vacuum pump or a very big dry sump type of pump to pull pan vacuum. A normal belt driven external oil pump isn't going to pull any pan vacuum.

[steve316]

I have a peterson wet vac about 6 in of vac. You will need to add a vacuum pump if you want to pull any vacuum.

[Schurkey]

For all practical purposes, don't Buick, Cadillac, and Mopar B-RB have external oil pumps, which don't pull any meaningful vacuum?

[Walter R. Malik]

How many inches of vacuum would you expect to see on a bbc with a full length pan? Would higher oil pressure affect the vacuum, if any?

I would expect no difference from an internal oil pump.

I would expect that type engine to pull around an inch of intake manifold vacuum at Wide Open Throttle on a dyno.

[MadBill]

Just in case it's not clear from the preceding posts: it is not possible to create crankcase vacuum via a single stage oil pump, no matter where it's located, as it cannot suck and blow at the same time* (*selectively draw in blowby gases and near-100% liquid oil and somehow dispose of the former while recycling the latter through the bearings, etc. back into the pan).

[user-23911]

If you want to be able to pull a vacuum, not only do you have to pump oil but air too.

An oil pump only pumps oil and all the oil goes back to where it started from so no vac created.


Another example of "common sense".

[ptuomov]

If you want to be able to pull a vacuum, not only do you have to pump oil but air too.

An oil pump only pumps oil and all the oil goes back to where it started from so no vac created.


Another example of "common sense".

And the air that is pumped out of the crankcase would have to be pumped somewhere else other than back into the crankcase!