Power Valve Size?
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Senior User
Joined: Jan 2002
Posts: 109
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From: Green River USA
Power Valve Size?
Hey guys is there a way to figure out what size power valve you need? My dad said you take vacuum measurements at idle and WOT and you do something with the number (he doesn't remember) to figure out what size power valve you need. I was thinking a 4.5 or a 5.0 but I don't want to jump in yet. I am at approx 6100 feet and I am a little rich, but I intend to order new jets along with the power valve. Thanx.
Posting Guru
Joined: Aug 2000
Posts: 1,127
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From: (near) Denver USA
Power Valve Size?
jdawg78,
Vacuum at WOT will be near zero.
If you want to be scientific, hook up your vacuum gauge and drive around with it. Note what throttle position you want the power valve to kick in and note the vacuum at that throttle position.
Changing power valves is not hard, and power valves are not expensive. I would suggest starting with a 4.5-5.0 in/Hg single-stage valve and see how it works. You can always try another one if you don't like the results of the first, and it might take a little trial-and-error experimentation to get the performance you really want.
Vacuum at WOT will be near zero.
If you want to be scientific, hook up your vacuum gauge and drive around with it. Note what throttle position you want the power valve to kick in and note the vacuum at that throttle position.
Changing power valves is not hard, and power valves are not expensive. I would suggest starting with a 4.5-5.0 in/Hg single-stage valve and see how it works. You can always try another one if you don't like the results of the first, and it might take a little trial-and-error experimentation to get the performance you really want.
Senior User
Joined: Jun 2002
Posts: 263
Likes: 0
From: Blackville, SC, USA
Power Valve Size?
The best thing I've done so far is get rid of the power valve with a power valve block off. Maybe I never used the right one but I like the carb. a lot better without a power valve at all.
Lead Driver
Joined: Nov 2000
Posts: 6,624
Likes: 342
From: Albuquerque
Power Valve Size?
A properly functioning power valve in the primaries is a "good thing" if you don't want to lean out when you lean on it. Check your vacuum at idle (in gear with an auto) and use a valve that's about half that number. (I idle at 14/15 power valve at 7). If the valve is higher than idle vacuum it will open and load you up.
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