Just purchased a used 565 BBC, has a Aerospace Vacuum pump on it and I was just curious as to what the readings should be at idle and downtrack.

My MOROSO 4-Stage Enhanced Vacuum pump on my SDPC 582 Head Hunter engine on alcohol is around 6" at idle and around 15" down track.

IHRA ACDELCO Canadian Nationals
Top/et Iron man Champion
Don Davis 57 Corvette Super Gas roadster
SDPC 582 Head Hunter on alcohol

Moroso (4) Enhanced. 12" at idle... 15" at 7400.

Yea this ones is like 1.5 at idle and up to around 3 to 6 downtrack

The number at idle tells you how well your engine is sealed up. The down track numbers tell you how well your engine is sealed + how good your vacuum pump is working. Drive ratio, fuel, pump type and size, and air leaks all come into play.

Ill play along. Have 11 at idle and 18 downtrack

Yea I dont think the previous owner ever adjusted it and just left it how it came from aerospace.

Moroso three vane enhanced driven at 50% with radius tooth pulleys and alcohol carb. Pulls 5" at idle and the vacuum break is set to pull 12" down track. The break isn't close to being maxed out so I assume I could pull more if I wanted.

quote:

Originally posted by SmokinChicken:
Yea I dont think the previous owner ever adjusted it and just left it how it came from aerospace.

yeah, i don't think that is it. If the max vacuum was set at 6 then it would have 6 at idle and 6 down track. I have a big electric vacuum pump that i use to check engine seal and i will bet that if i hooked yours up, it would be whistling like a sailor on payday getting ready to visit a hooker.

Joe

Motor is consistent, repeats back to back.

I didn't say it wasn't consistent. I said it would leak a vacuum. this happens if they put a "stock" single lip seal that lets air in when under vacuum. It could be the crankshaft rear or front seal. but with that low of a vacuum you either have some sort of pump issue or a leak.


Joe

My Star setup is 5 at idle ad 12 downtrack. We didnt use any special crank seals or flip them.

I had one aerospace pump and it never pulled that much vacuum. At times 0 at idle and 2-3" downtrack. I switched to the moroso pump and it worked a lot better. I get 5-6" at idle and around 11-12" downtrack.

Be real careful about going over 15" down track. You can start pulling oil away from the rod bearings. Remember that the oil pump and vacuum pump are fighting each other. I have a 555 and normally see 6" at idle and 14" down track. I could turn it up but I don't. I use a Star.

Star vacuum pump here....I just make sure my engine is sealed and cranked the regulator all the way down!!! No issues at all with oiling, solid oil pressure on and off the throttle! Bearings looked really good last freshen!

I honestly don't know how much I'm pulling....still trying to get the graph to come up on the grid but I think I figured it out with markemark's help!

8 idle
10 run regulated
4 vane enhance moroso driven a little faster
With 15 psi boost

People that I respect in the industry warned me about exceeding 13-14 pounds of vacuum. There is very little if any power gain in going higher but there is a real chance of drying the wrist pins and/or depleting oil from other important components, bushed lifters, bearings, etc. I'm more than willing to concede that small power gain in exchange for greater reliability.

I've watched a few Pro Stock Teams cut/remove the dry sump belt prior to the last round trying to gain a little more power.

Bob

Bob,

A vacuum of 13-14 PSI is around 27" of mercury, practically a soft vacuum as the ambient air pressure is only 14.7 PSI or 29.92" of mercury.

Also cutting the belt to the dry sump cuts all scavenging and pressurization of the oil system as they all share a common shaft.

Not sure what you might have saw but I don't think someone is going to find much power by cutting a dry sump belt.

Ryan

My aerospace pulls around 3 at idle and 8 down track. it keeps my oils clean and thats the only reason I have it.

I believe that David Reher mentioned being careful about exceeding 14-15 in one of his shop tech articles, I was not willing to test his theory based on my budget and particularly in the throttle stop class car (S/G and S/C). I don't doubt your opinion Ryan, in fact quite the opposite.

As for the dry sump belt, it was what I witnessed, don't know why just that they did cut the belt.

Bob