What effects have you seen on oil pressure when running a vacuum pump. At what amount of vacuum did you see changes. How much is to much and whats not enough.
Thanks

My electric pump (GM-style) pulls about 5" and did not affect oil PSI. It eliminated the exhaust smoke I was getting from my low-tension rings.
I've heard that somewhere above 15" or so that it causes oil shortage at the wrist pins, but I can't confirm that; I'm sure a REAL engine-builder will chime in.

That is the canary in the mine--wrist pins get killed --you were too far. Usually for a "Fuse" run a cheapo valve cover gasket not glued in place. It will pull them in before you kill the pins. A little vacuum is good and helps any engine. Good gains can be made with less than you think.
It cost a ton to run a vacuum pump and unless you have a sloppy big bore pro type engine or Need that extra few ponies in a limited class etc it is a luxury that most bracket guys can live without.
Most "all out" builds wind up with one but the average bracket car --it is not a good dollar vs. HP investment.

On a wet sump system the vacuum pump will decrease the oil pressure since there is less "pressure" pushing the oil into the pump. You can do the math to figure it out. Just convert inches of vacuum to pounds of pressure.

Thanks this is good info. I did not know the inches of vacuum to psi conversion. This solves some of my mystery. Andy we talked about oil pressuer and liftes a few weeks back. I believe I know where I'm headed with this now.