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Old 01-22-2020, 12:03 PM   #1
19Fordy
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Default What size power valve should I use?

I have a Holley 390 4 barrel 4160 carb. List #0-8007.
Standard 1940 3 speed transmission.
No A/C. or any other amenities except vacuum wipers.
1953 Ford V-8 239 cubic in. stock engine.

Vacuum reading at idle is 18.
Jets are #49

What size power valve do you suggest?
The stock Holly came with #51 jets and 6.5 power valve.

However, I read that the recommended power valve should be obtained by dividing the vacuum reading at idle by 2. Is that true? Thanks.
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Old 01-22-2020, 02:00 PM   #2
1948F-1Pickup
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Default Re: What size power valve should I use?

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What you read is true. And....
"if your divided number falls on an even number, you should select he next lowest power valve number"

By "the book" you'd use a 9 for a power valve, which isn't available.
A 9.5 might be a little aggressive. (Every time the vacuum drops to 9.5 Hg, it's going to open)
You might like the engine more under load before the PV opens, so a lower numbered power valve like an 8.5 or 7.5.
(hook up a vacuum gauge and see where the reading goes as you're driving)
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