holley carb Question
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holley carb Question
Im looking to get a bigger power valve for my holley 390. summit sells them and they offer single stage. double stage, and high flow. can anyone shine some light on what the differences are. my intake vac at idle is 19 so im going to go with the 8.5 p valve. also do i need a special tool to get it off. hard to change??
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Joined: Dec 2007
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From: Boise, Idaho
The dual stage are more for gas mileage and not for performance (generally for larger vehicles, or those with really tall gearing) and will open partially at higher vacuum and fully at lower vacuum (such as a 5.5/11.5hg)
The high flow are for racing engines that you pretty much just want to dump fuel into.
I don't remember the physical size of the powervalve, but I usually just take mine of with a standard adjustable crescent wrench. They just need to be snug, and not torqued down.
To change them, unbolt one of the bottom bolts on the primary side fuel bowl and drain the fuel out (I usually use a plastic cap, such as one from a WD-40 can), and then remove the other three bolts. Pull the fuel bowl off and the main jets should be visible. You can just pull the metering block off by hand and the power valve will be on the other side.
The high flow are for racing engines that you pretty much just want to dump fuel into.
I don't remember the physical size of the powervalve, but I usually just take mine of with a standard adjustable crescent wrench. They just need to be snug, and not torqued down.
To change them, unbolt one of the bottom bolts on the primary side fuel bowl and drain the fuel out (I usually use a plastic cap, such as one from a WD-40 can), and then remove the other three bolts. Pull the fuel bowl off and the main jets should be visible. You can just pull the metering block off by hand and the power valve will be on the other side.
Cargo Master
Joined: Sep 2007
Posts: 2,095
Likes: 2
From: Wahpeton ND
Have a new set of both fuel bowl and metering plate gaskets on hand. Holley makes about 4 different styles of meetering plate gaskets so make sure you have the right one.
The high flow power valve will do nothing to improve performance in a carb that dosent have the larger fuel ports to utalize the larger ports in the HV power valve. It will do nothing bad or good as the power valve restriction ports will limit the fuel flow through to the engine. One can drill them out to realize the potential of the HV power valve but it is unnessisary in a street engine.
The high flow power valve will do nothing to improve performance in a carb that dosent have the larger fuel ports to utalize the larger ports in the HV power valve. It will do nothing bad or good as the power valve restriction ports will limit the fuel flow through to the engine. One can drill them out to realize the potential of the HV power valve but it is unnessisary in a street engine.
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