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I have a 434 sbc with nitrous...alot of nitrous 450hp worth. I am not running a relief valve using my Moroso 3 vane pump. How much is this hurting me?
4" pump pulley, 2.5" crank pulley
 

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You may find that with a three-vane pump, what vacuum it does pulls, won't be excessive not regulated.

My four-vane Moroso w/relief is set to pull 12-14 inches at 7000 rpms. On a 406 s/b, with a wet sump oiling.
 

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With a three vane with the 4" pulley and the 2.5 on the crank you will only get 10-11 inches. If you went to the 5" pulley on the pump you will get 12 inches. That is what I seen on the dyno.
 

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I wouldn't run it like that much longer. You're prolly starving the wrist pins. Put a vac. gauge on it. Tap the bottom of the intake or a valve cover if your sealed upi good. I'd have 16"s on mine without a relief and I'm on methanol. Even though you're stating the max rpm that really doesn't matter as you will likely pull max vac. way before that. Ideally you want max vac at launch. Every motor is different so I'd get a vac gauge on it before running it next.
 

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I wouldn't run it like that much longer. You're prolly starving the wrist pins. Put a vac. gauge on it. Tap the bottom of the intake or a valve cover if your sealed upi good. I'd have 16"s on mine without a relief and I'm on methanol. Even though you're stating the max rpm that really doesn't matter as you will likely pull max vac. way before that. Ideally you want max vac at launch. Every motor is different so I'd get a vac gauge on it before running it next.

What brand pump and 3 or 4 vane?

On alky too and have been running the vacuum pump pulling 12-14 for eight years with no wrist pin issues and my pins are not coated. I'd have to say you are getting into "risky" territory at 16 inches depending on your piston/pin clearances.

I do agree that max vacuum will happen long before max rpm.
 
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