Power Valve on the Holley

[Doc Voodoo]

Ok I rebuilt the old holley . The Number on the front of the choke chimney is 1850-2. 600CFM the Jets Are both 66
When we rebuilt it the kit came with a 7.5 power valve. It did not alow for any adjusting and was running way to rich. The original was a 6.5 . Well we picked up what I thought was a tuner Kit but it did not have any 6.5 power valves in it. It did have a 5.5. So we tried that. I noticed a power loss that got worse on the top end.

Now I know I have read in order to tell what you need for a power valve you need to measure the vacuum as your going down the road what ever that reads you subtract 2 from and thats your power valve seting.


Now does the vacuum go down the more you make it breath the reason I ask is that I have not put my headers on yet and the engine is modified with the HR274 comp cam and 351 sized valves in 289 heads. Right now it has regular old 289 exaust manifolds. So its not truly breathing yet.

When I put them on will that change my power valve needs. Right now it looks like I need the 6.5 .

 

[68GEETEE]

not sure if this helps but........ http://community-2.webtv.net/MATTGRU/HolleyPowerValve/

 

[Max Power]

While the vacuum down the road theory is basically sond, cars with a lot of cam don't carry much vacuum at idle. You may have been tipping into the 7.5 at idle, causing a rich condition. Since you know that the 6.5 ran well before, use that until you do your mods. You should be able to buy power valves solo. I always have a few on hand.

 

[Doc Voodoo]

ok so with less Vacuum " do to the Cam " I should go down or up on the power valve # scale ?

 

[Max Power]

The number on the power valve is the vacuum reading that it will open and begin enrichment. If you have a 7.5, it will open when vacuum is below 7.5, which sometimes occurs at idle on lopey cammed cars. The 5.5 would reduce that number to 5.5 inches of vacuum before it opens. Again, if 6.5 worked before and you have made no other mods, that is what I would go with.

To my recollection, the power valve should not effect top end performance at WOT, as you are in low vacuum situations either way, and either valve would be open. All the power valves should flow the same.