I have an older Moroso pump, four vain. I have gotten 10.5 inch vacuum in the past without any bleeder to control vacuum level.
With the new build, I had problems getting 3 or 4 inch vacuum, but am not sure why. My moroso pump has maybe 300 runs on it, is 18 years old. The fittings are 90 degrees apart ,not the newer 120 degrees.
My new short block will have DLC coated piston pins, so that area is covered. I am Looking for info on how much vacuum to run, and anything I should know to stay out of trouble. Thanks in advance, Greg

I know racers with both dry sump oil system and those with a vacuum pump that have 17+ inches of vacuum idling and at the upper RPM at WOT, they swear by it Mine barely pulls 5.0 at idle or revved up

If one motor won’t pull vacuum with a similar pump there has to be a leak. Either ring seal, lip seals, or gaskets. The GZ pump on mine pulls around 10. I’ve pressure checked it with low air pressure. Then sprayed the entire motor with soapy water. No bubbles anywhere. I’m pretty sure my ring seal has been good. That leaves the possibility of not sealing under vacuum. That would lead me to believe either the Jessel cam/crank seals (new made zero difference) or the rear main seal. Thinking about installing the double lip rear main seal.
Doug

In order to get my motors to really seal up I have to smoke test them and I always find leaks I have to fix.

I use a cheap smoke tester from Amazon:

https://www.amazon.com/AutoLine-Pro-Automotive-Diagnostic-SMK-1/dp/B06XHRBKTM

With a Moroso four vane pump a sealed up engine and low leakdown I have to use a regulator to get it down to 12 inches.

I agree, same pump different engines the problem is probably with the second engine.

Might tear that old pump apart and rebuild it. We use a 4 vane on the vette and are at 20"+ I use them on my junk too and we are 15-17 depending on the engine its on. I think the dragster could likely use something better maybe. But we have some ither issues to fix in regard to vacuum there. I also have a Star pump and it's a very nice piece for sure but the results are similar. We don't regulate vacuum with any of them and never seen any issues with the loads we pull.

On my B1 540 wet sump and Moroso Enhanced 4 vane setup I was pulling 15-17” and keeping a close eye on it. With my 412” Canted Valve head SBF, 4 stage dry sump and Moroso 4 vane I was pulling 21-23”. Not every application needs a vac pump, but all applications will benefit at making more HP, especially when setup for vac pump use.

Greg, like Al suggested, freshen up your pump, it’s probably time.

Are you guys that are getting 10-20" of vacuum installing your rear main seals backward?

While your vacuum pump could be worn, I have found It's best for me to check the crankcase for leaks. Before installing the motor I pressurize the crankcase with about 10 LBS of compressed air. I've also done it with the motor in the car but it can be difficult to find a small leak and seal it.

I've never installed the crank seal backwards. My Ritter block has a special rear seal. With my X and R-3 block they pull decent vacuum maybe 10-15" with the seal installed normally.

There are better seals out there for sure. But I have not seen a lot of difference with them. I dont put mine in backwards never have. Making sure its sealed well is the key. If you are constantly putting OIL in the puke tank you have a leak!

I've been told the rear seal breaches around 12". I don't measure how much my 5 stage pump draws but, I know I have vacuum! lol I put my lip rear seal in in the conventional way. I figure, even at 12" I'm getting a good chunk of what I need.

I have a 4 vane Moroso I bought used 8 or 9 years ago and it's been great. It pulls around 10". Have the same pump on the Camaro and it's been on that car for nearly 20 years, but it's been rebuilt a couple of times.
Main seals put in the conventional way, low tension rings, etc.

I bought the Moroso after my 2nd Aerospace Components pump $h!t the bed. It would pull 7" at best w/ the regulator closed. Aerospace sucks.

Thanks everybody. I ordered a smoke/leak detector listed above. One step at a time, check the current pump for ware, seal the new motor well, go from there. I found a 4.5 inch pulley available from GPZ that fits, speed increase of 11 percent. Try that . If I don't t reach decent vacuum of +14 inch, the expensive fix is a 4 vain enhanced, which is supposed to reach good vacuum when staged.