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Discussion Starter · #1 ·
i just searched all "vacuum pump" posts for the last year and learned a little but not all i need. my street driven 408 ford has a gz pro pump driven at 60% and the relief valve allows for about 8" of vacuum on its loosest setting. the pump shows no vacuum at idle but with the relief valve i can turn it up to make alot. the gz setup uses 10an hoses. i suck out of the driver's side vc and it is baffled well. my relief is in the passenger vc. my puke tank is lower than my pump. the pump will fill the puke tank with oil after about 40 miles of street driving. i believe that i may have a vacuum leak in the motor. what is the best way to find/look for this? i had a header evac setup but noticed a small rear main leak and got the vac pump to help this, which it seems to have fixed. thanks john
 

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I'm not a fan of running 8" of vacuum for 40 miles of street driving.

honestly, I don't have any experience with trying to run this kind of vacuum in a street condition, as I have always tried to steer folks away from it.... I'd like to see it limited to just enough that the crankcase will be cleared out.... 2-3" max... with a pressure valve on the valvecover in case the crankcase goes positive....

Best way to check for leaks is to fill the engine up with air pressure.... obviously, within common sense limits.
 

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Plug the valve cover relief and move it to the line.
Instead of alway drawing through the motor you can feed the pump with cool clean air.
8" is alot for driving a couple is fine while on the street.
 

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Discussion Starter · #4 ·
it doesn't make 8" until about 4k rpm's. what about using a smaller crank pulley and driving the pump at 40%? what will changing to -12 lines do? i am considering changing the inlet to the pump from the top of the vc to the front and i am definitely moving the relief to the pump. sorry for so many q's. thanks john
 

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it doesn't make 8" until about 4k rpm's. what about using a smaller crank pulley and driving the pump at 40%? what will changing to -12 lines do? i am considering changing the inlet to the pump from the top of the vc to the front and i am definitely moving the relief to the pump. sorry for so many q's. thanks john
Move the relief and do a leak down test too1
 

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Discussion Starter · #8 ·
update- now sucking out of the front of the valve cover, instead of the top, have star relief valve on the pump. 3" at idle, 10" at 4500 rpm's. sucks zero oil and the rear main is dry as a chip. next step is to put on a smaller crank pulley and slow the pump down to 40%. i'll let you know. thanks john
 
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