Power Valve Size - Team Camaro Tech
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post #1 of 5 (permalink) Old Apr 10th, 08, 07:05 PM Thread Starter
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Dustin
 
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Power Valve Size

I bought a motor about a month ago and the guy suggested getting the carb rebuilt. So I got the carb back about a week ago and the shop rebuilt it back to stock specs. I was wondering if with my motor specs I could get an idea of the correct or close to correct power valve size? The motor is not in the car right now and on an engine stand, but I would like to get the carb close as close to ready as possible.

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post #2 of 5 (permalink) Old Apr 10th, 08, 07:33 PM
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Don
 
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Re: Power Valve Size

Looks like a HP 850 holley Vs would work well. Pv selection is usually determined by your engine vacumn, being not everyone uses the same cam.. Usually two numbers below your best idle vacumn. Ie, If you idle in gear (AT) is 10 hg then a 7 or 6.5 is your selection. 6.5 is usually a norm in most hp cars.

What carb do you have?

Don
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post #3 of 5 (permalink) Old Apr 10th, 08, 08:47 PM Thread Starter
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Dustin
 
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Re: Power Valve Size

HP 850 w/ MS, MS since I am running a TKO 600

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post #4 of 5 (permalink) Old Apr 11th, 08, 07:16 AM
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Don
 
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Re: Power Valve Size

Quote:
Originally Posted by 01somta View Post
HP 850 w/ MS, MS since I am running a TKO 600
This will work, Pv front and rear , should be about the same.

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #5 of 5 (permalink) Old Apr 12th, 08, 09:09 AM
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Re: Power Valve Size

There is no formula to tell what you need for sure. Using an A/F gauge helps to see where the extra enrichment is needed.

You want to tune the carb on the jets at a series of speed up to about 60 mph. Jet down until there is a surge present, and then jet up 1 to 2 sizes from the surge. Then set your PV and PVCRs. There is a lot more to it than that, but these are the basics.

The powervalve is an extra fuel switch. It needs to turn on when engine load is high enough that the engine wants more enrichment. Finding the point this happens isn't easy as there are a lot of circuits working together around that point.

Most likely I think you will need a 6.5. But you didn't list much relevant info to make a choice. Idle vacuum in gear, park, and at cruise at various speeds would help get closer to what you need.

As far as running primary and secondary valves, you have to test and tune. On a hard launch a secondary PV will get uncovered and not have enough fuel. Most people with drag cars plug the sec. PV and jet up 6 to 8 sizes on the secondaries. If you are looking for economy too you can use a sec. PV. You can either run the smae inch value or stagger the PV settings. If you stagger, you can run say a 6.5 in the front and an 8.5 in the rear. Again, it is what the engine wants at various loads, speeds, and how you give the gas pedal.
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