How much vacuum do you try to pull with a belt driven vacuum pump. Can you pull to much the car I bought has vac pump but it's got a relief in the valve cover that you can adjust. Thanks

If the engine wasn't built for high vacuum then I'd set the relief valve around 8 to 10 inches of hg. Engines that are built for high vacuum can pull a lot more. I think the NASCAR boys pull 20 inches of vacuum. You really have to build a tight engine to pull that much vacuum. Most bracket type engines are not sealed up well enough to pull very much vacuum.

To bounce off what Andy stated, MOST bracket engines will not be capable of making anywhere near 20" of vacuum, many pumps out there also will not build 20"
either, especially with a wet sump oiling system. FWIW we run a Moroso 3 vane on the dragster and make 14-15" my car is an enhanced 4 vane and can see 19-20", we run both unregulated, both were built to run a vacuum pump. The heads up car we can get 22" with a wet sump, that's a very high number on a wet sump. Most bracket engines will be 8-10". Is there power there, that is debatable but you will eliminate any pesky oil leaks for sure.

I run the Moroso four vane also and set it for 12" . I have seen it as a high as 16" I don't know if that is the max or not.

I try to keep it at 12" because of probably unwarranted fears of galling piston pins.

It is hard to get everything sealed up. I have a cheap smoke machine I got off either eBay or Amazon that is a big help.

Same here. MUCH better pump than the POS Aerospace pump I had before.

These are the seals I run., double lip...the rear main seal highest qualty seal I have ever used and the seals they offer for jesel drives are just as nice....I run a older moroso 5 stage dry sump pump and a product eng. 5 vain vacuum pump. I’ve seen 23” of vacuum. vacuum =power

My problem I see is when I crank on my vacuum pump knob is the higher the vacuum goes, my ok pressure drops significantly which makes me uncomfortable.

to get and maintain high vacuum with out problems, requires a lot more than just seals to seal up the engine. I have never seen my motor ever fall below 85 psi during a run....

I try to not run more than twelve. my engine builder is worried that it might pull oil away from the piston pins and rings.

Your oil pump is still working the same so your bearings still have the same oil pressure, the gauge reference point has just been moved.

I learn a long time ago on wrist pin clearance a tiny bit to tight is no good, IE .0010 clearance or less on any stock BB Mopar wrist pin is to tight
On my motors using BB type Chevy rods with .990 wrist pin size I ask the machine shop to make sure they have .0010+ clearances I base this on .0010 oil clearances for each inch in diameter on any rotating wear surfaces in our motors

I only run about 11hg. Id run more in a heart beat. My bet is its pulling air at the rear main seal. Oil pressure is a function of atmosphere over flow. The number goes down if the atmosphere isn't pushing on the level in the pan. Turn the pump up. Next time its apart the rear seal Boat Racer suggests will be in it.
Doug

As stated your oil pressure is not changing. Just the reading is and I find most guys run WAY to much oil pressure anyway. Not that its a bad thing as I have done both just seems most run more than necessary for sure.