Power Valve - correct size? - Team Camaro Tech
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post #1 of 9 (permalink) Old Jan 16th, 10, 06:30 AM Thread Starter
Dan
 
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Power Valve - correct size?

I have a '67 Camaro with a 350 that pulls 19" of vacum at idle. I'm running a Holley 670 Street Avenger carb. What is the correct power valve size pulling this much vacum.
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post #2 of 9 (permalink) Old Jan 16th, 10, 07:35 AM
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Don
 
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Re: Power Valve - correct size?

I would guess you have an 8.5 or 10" pv in there now. PV is needed when you are demanding more fuel or power and does just that, opens up at a lower vac setting, its basically fuel transition between the idle circuits and main circuits. You could pull off front bowls and remove metering block to check. Be sure to have a set of gaskets , just in case you tear the orginals. You may luck out and you carb may have those non-stick gaskets.
Rule of thumb is generally to run a PV with a setting, 2"hg lower than idle. Sounds like you have a stock set up so you are a long way from the PV opening point.

Cam?

Don
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post #3 of 9 (permalink) Old Jan 16th, 10, 07:52 AM
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Re: Power Valve - correct size?

This is one of the few true articles I've seen about a power valve...http://community-2.webtv.net/MATTGRU/pv/ Your vacuum at idle has absolutely nothing to do with the power valve. You must drive the car with a vacuum gage and find out what the motor wants and when it wants it.
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post #4 of 9 (permalink) Old Jan 16th, 10, 10:25 AM
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Re: Power Valve - correct size?

Are you having driving issues ?

68 Camaro~LSx ~all motor
1.54 60'--6.95 @ 98.45 660'--10.96 @ 121.53
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post #5 of 9 (permalink) Old Jan 16th, 10, 11:07 AM Thread Starter
Dan
 
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Re: Power Valve - correct size?

I'm in the process of tuning the carb. It currently has a 6.5 power valve and I know with 19" vacum that that must be to small. I don't want to tune around an incorrect power valve size....meaning I don't want to increase the shooter and/or main jets because of a bog or hesitation or other condition when the condition may actually be caused by the power valve being to small.
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post #6 of 9 (permalink) Old Jan 16th, 10, 11:24 AM
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Dan Ensign
 
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Re: Power Valve - correct size?

The number on a power valve does not determine size, it is the inches of vac. that it opens at as vac. in the intake drops under accelleration. I have always used the manifold vac. at idle spec. divided by 2 to determine the proper power valve.

Dan E.
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post #7 of 9 (permalink) Old Jan 16th, 10, 11:44 AM
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Don
 
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Re: Power Valve - correct size?

To add to what Dan said, 25, 35, 45 65, 85" hg range power valves do not measure fuel,l they measure vacumn and they open main fuel circuits on vac signals that comes from the engine to in turn open the pv to allow more fuel to pass.
Now, if your main jets are too small, then you increase them, not the power valve. The 19'' vacumn you are reading has nothing to do with the pv at idle. You need to install a temp vac gauge and long hose into the cabin of vehicle and drive the car, You need to monitor it and see what the vac is , when ever , with what ever problem you are having. This will tell you a lot.

With this much vacumn, I am wondering where your inital and total timing is .

Your stumble could also be linked to vacumn secondary opening as well as accel pump shot, linkage and pump cam. I think the new avenger carbs have the adjustable vac diaphram that can allow early or late opening.

Also, as Doug asked, what problems are you having? Also, read this , maybe it will help . http://www.holley.com/data/TechServi...wer_valves.pdf

Don
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Last edited by zdld17; Jan 16th, 10 at 11:57 AM.
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post #8 of 9 (permalink) Old Jan 17th, 10, 05:44 AM
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Re: Power Valve - correct size?

Are you checking this with the car in gear at idle or in park?Is it possible you have a vacumn leak somewhere?


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post #9 of 9 (permalink) Old Jan 17th, 10, 06:40 PM
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Re: Power Valve - correct size?

Quote:
Originally Posted by markw View Post
This is one of the few true articles I've seen about a power valve...http://community-2.webtv.net/MATTGRU/pv/ Your vacuum at idle has absolutely nothing to do with the power valve. You must drive the car with a vacuum gage and find out what the motor wants and when it wants it.
I am behind markw^ 110%.
I have externally referanced power valves that allow me to dictate vacuum at idle with a hand held vacuum pump.I can tell you that opening and closing a power valve has no affect on my wide band a/f meter that responds in synch to even the slightest adjustments made to my curb idle mixture screws.
Forget about pv sizing on the street unless you have an in car vacuum gauge that you monitor while transitioning thru the carb ckts.
Fwiw..my pv opening points are higher than my at idle vac #,s.Who cares if their open at that point.The added head pressure in the main well with an open power valve has a tiny effect on the idle feed restrictor if any.

George
68 Camaro
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