Power valve opening, Holley carburetor


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By patm - 12 Years Ago
Out of eight new power valves (PV), Two open within a 1/2 inch of rated vacuum; others opened at two to three inches below what is rated. Most recently, I purchased two holley PV, 95 & 75---75 opened at 70 & the 95 opened at 60. I used a Moroso PV tester and a dial indicator. PV names are Quick Fuel, Holley and unknown. I did the tests several times with the same results.

Curiosity got the best of me and I kept buying PV. I am looking for comments; am I doing something wrong?

These PV have not been installed in a carburetor, as yet.

Thank you, Pat.
By Talkwrench - 12 Years Ago
Well I have to ask .... Why are you doing this Pat? Usually ballpark is ok for P/V's If you have a good strong vacuum at cruise and all is well you would put in around a 8.5 .. I've even had 10.5 no great diff [ Holley 4 barrel]
By patm - 12 Years Ago
I did it because I was curious. Perhaps I am being overly picky and I should accept the average, the ballpark.

Thank you for your suggestion, Pat.
By Talkwrench - 12 Years Ago
Couriosity only killed cats. Tongue
By Talkwrench - 12 Years Ago
I must say its not showing good quality is it..
By Ted - 12 Years Ago

As this thread is a better fit in the ‘Technical’ section, it has been moved accordingly.

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A ½” Hg variance in power valves opening as measured to their rated value would be normal. As a general rule, I do find that new Holley brand power valves open very close to their rated values. A 2-3” Hg difference between the actual opening value and the rated value could pose a problem on an engine that is by design running at a lower than normal idling intake vacuum number. Kudos to you for checking the power valves before installation as that does help to eliminate one more problem that could potentially crop up if not done so. If you find a particular power valve manufacturer that is consistently having a discrepancy in their power valve opening values, then dropping them a note about the problem may help to get that resolved for the rest of us down the road that happen to use those particular valves.

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I’ll add that as the Holley style power valves age, the rubber stiffens which in turn alters the opening rate and can get so stiff that they don’t close at all. Once the power valves are about ten years old, they should be changed out for a new ones.