@@futten3230 I was in the mechanical refrigeration field for over 20 years, I will agree with you that yes you can have positive and negative pressure. But the standard way of measuring manifold vacuum on a racing engine is in inches of mercury. That’s why Holley power valves are sized between 2.5 and 10.5 Hg so you can match the manifold pressure to the correct power valve. The original post was made because the video said Holley power valves are measured in PSI, and they are not. But thanks for adding to the discussion. By the way, the symbol Hg stands for Hydrargyrum which is Latin for Mercury. Thus measuring in Hg means inches of Mercury.
I'm drag racing with a Q-650, the idle vacuum is 13, At WOT the gauge reads 4.5 inches of vacuum. Is the 4.5 stock power valve only starting to open then? Is the power valve just on the verge of opening at 4.5 vacuum and will it then give inconsistent ET's?
S Sterley of you have 4.5" of vacuum at wot your carb is too small. Wot vacuum should be 1-1.5" . And yes 4.5 power valves begin opening at about 4.5" of vacuum.
A power valve is a crude way of in changing the jetting via the vacuum on the carburetor, Either Quick Fuel or Holley's, they or not for gas mileage. Power valves have no metering, just open and close and that's it. Want good gas mileage get a Carter / Edelbrock AVS or thremo-Quad / Demon or a Rochester, not a Holley or Quick Fuel.
Manifold vacuum is not measured in PSI.
Power valve are not sized in PSI.
you have negative and positive PSI
@@futten3230 I was in the mechanical refrigeration field for over 20 years, I will agree with you that yes you can have positive and negative pressure. But the standard way of measuring manifold vacuum on a racing engine is in inches of mercury. That’s why Holley power valves are sized between 2.5 and 10.5 Hg so you can match the manifold pressure to the correct power valve.
The original post was made because the video said Holley power valves are measured in PSI, and they are not. But thanks for adding to the discussion.
By the way, the symbol Hg stands for Hydrargyrum which is Latin for Mercury. Thus measuring in Hg means inches of Mercury.
I'm drag racing with a Q-650, the idle vacuum is 13, At WOT the gauge reads 4.5 inches of vacuum. Is the 4.5 stock power valve only starting to open then? Is the power valve just on the verge of opening at 4.5 vacuum and will it then give inconsistent ET's?
S Sterley of you have 4.5" of vacuum at wot your carb is too small. Wot vacuum should be 1-1.5" . And yes 4.5 power valves begin opening at about 4.5" of vacuum.
If you getting 4.5 at wot you need a bigger cfm carb
Others are saying you need a larger carb, but you didnt say if you drive the car much or just race it.
A power valve is a crude way of in changing the jetting via the vacuum on the carburetor, Either Quick Fuel or Holley's, they or not for gas mileage. Power valves have no metering, just open and close and that's it. Want good gas mileage get a Carter / Edelbrock AVS or thremo-Quad / Demon or a Rochester, not a Holley or Quick Fuel.
I cant beleive you have a girl spiting out powervalves, not even looking at them. Are you alright or what.
are you? cause i dont see the problem with having a female doing the job they are just as qualified as men