Pan vacuum issue

[BlitzA64]

I am running a 4 stage Barnes Dry Sump Pump (Gear) that has 1.5" scavenge sections, all 3 from the pan circle track. I am having trouble getting any vacuum, in fact getting a bit of crankcase pressure. Engine is fresh, leak down good, pump has maybe 2 hours run time on it. I have seen a few posts about pulling 8" or so with a 4 stage just wondering if I should bit the bullet and go with a different pump or maybe try changing plumbing and pan

[Kevin Johnson]

I just looked through your posting history and you have a lot of experience with dry sumps. Have you run this same engine/system using a different setup?

[BlitzA64]

I always have run injected alky, never tried to pull pan vacuum with those engines. This is carby gasoline so I figured I would find a few ponies sealing it up. The other carb gas motor I ran we put a 6 stage pump on it, 4 from the pan and 1 in the valley. No problem getting vacuum from that one. I think this pump is just too small and loose to do what I want. I was thinking maybe running 2 in the pan and 1 in the valley might help but I doubt enough to pick up anything. I should go to more pump and call it a day if I want to get some vacuum

[BlitzA64]

Another issue may be I am running the pump off of the cam, only 50% with that. If I had a belt I could overdrive the pump some to help

[MadBill]

What do you see for vac. if you slowly rev it up out of gear? A 380" SBF with a 5 stage Aviaid pump I consult on pulls as much as 18" with the check valve cranked right down. (we usually run ~ 12")

You can test for leakage by sealing up all external ports and connecting a gauge to manifold vac, teed to any convenient access point for CC vac. (E.g. one bolt hole on the front of factory SBC blocks ahead of the fuel pump pushrod is drilled through to the CC.) Fire up the engine, rev it up a bit if need be to get 20" or more on the gauge (or connect to another vehicle's manifold vac.), then pinch off the manifold line and shut down the engine. Alternatively, seal it up, pressurize it to 10 psi and use a length of hose as a stethoscope or use soap solution to track down leaks.

With no special crank seals, etc., the above SBF seals well enough to take 75-90 sec. to bleed down.

[BlitzA64]

I have an A/C vacuum pump I use for that Bill. I did not assemble this engine it was done at the machine shop and installed in a rush so there could be some issues there. It is building some pressure though which makes me think something is not right. I will pull the pump off and have a look see after the race next weekend, in the mean time I'll vent it and let her rip. I would "assume" if it starts to build pressure that would make things worse

[Darin D Morgan]

I am running a 4 stage Barnes Dry Sump Pump (Gear) that has 1.5" scavenge sections, all 3 from the pan circle track. I am having trouble getting any vacuum, in fact getting a bit of crankcase pressure. Engine is fresh, leak down good, pump has maybe 2 hours run time on it. I have seen a few posts about pulling 8" or so with a 4 stage just wondering if I should bit the bullet and go with a different pump or maybe try changing plumbing and pan

M humble advice is to run pump 1:1 crankshaft speed and vacuum check the engine. We pull a vacuum on the crank case and use a stethoscope to find small leaks around the engine.

[BlitzA64]

I will search out leaks next chance I get, thank you for replies