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Discussion Starter #1
Just checking because I don't want to hurt the pump, but I am only able to get about 7" of Vacuum so I just bought a 4" crank pulley to hopefully get me up around 12 or 13" . Just checking if anyone is doing this? A little information on engine is 572 co 15 to 1 with TR and dual dominators running about 8000rpm tks Jim
 

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wiith a 4 vane, we run 18t crank and 36 or 4o tooth pump, and get 15+ inches in a 23.9-24.2 baro. if you are running it that fast there is a leak, or poor ring seal. We run it at 50% or less crank speed. And typically have to take shims out of the pop off to keep it that low.
 

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Do you have a sealed dipstick tube?

(Adding a lb or so of air pressure inside the crankcase can help find a potential leak.)
 

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Discussion Starter #10
Do you have a sealed dipstick tube?

(Adding a lb or so of air pressure inside the crankcase can help find a potential leak.)
Yes I do
What size pulleys are on it now??
How old is the pump??
Pump is probably 8 years old and I checked the vanes and they looked ok but not new. I have a 5" pulley on pump and 2" on crank, And just put a 4" on crank.
 

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I will try that ty
also, make sure the pump is clean inside. Oil can stick the blades, esp at lower rpm. Is the vac low but linear going up the track? Typically thats a leak. If it starts ok, and falls during a run, that is more indicative or a ring seal issue. Ive also seen some of the AN hose will suck itself closed at higher vac. 7" shouldnt do it but its just a thought
 

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Used 4 vane Moroso's for years with good service. If you use oil additives, they're prone to the carbon paddles sticking and the the vacuum pull going down accordingly. I cleaned mine after every race by running brake clean through them. Good and clean they'd pull around 20-22 inches (on a good sealed engine) but I usually limited them to no more more than 18" on the 'puter.
 

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632 @ 10-12 here. When was the last time it had a kit put in it? And look inside the suction
side. See if it is milky.Mine when it gets a little milky, i do the ole brake clean deal and a shot of WD when done.Going on 7 years here with the same oem vein kit.
 
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