How do you determine the rating of a Holley power valve? I seem to remember that there was a number stamped into one of the flat sides of the hex but I can't find any markings on two that I have. Can anybody clue me in?

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If you didn't drive it there, it's not a street car.

Take a manifold vacuum reading, if its an auto do it in gear w E-brake on. Devide reading by 2 and that is the power vlve size that you need.

I just did this yesterday. 17Hg in of vac/2 = 8.5 pv

(EDIT)
Us a vac gauge w a suction cup to determan pv size.





,Cliff

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'72 4 dr Dart
'63 4 dr Dart

I have seen several that have the number stamped on the, (top??), sheet metal diafram cover.

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An officialis Tyrde-Browne Racing membrum

I seem to remember the shape of the window had a different shape for the gasket used.

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Part of Tyrde-Browne Racing

depsnding on the "era" the PV was made it can be:

1) stamped on the "plunger" side of the PV (I have one from the 90's that is stamped 7.5).
2) They can be stamped on the side, usually a 2 digit number like "95"
which would be a 9.5
3) They can two stamps on the face....one set is the "month and last digit of the year", the other is the PV number (sometimes hard to tell and August 2005 from and 8 5 PV... a 10.5 usually comes as a 0 stamped above a 5)
4) Holley "Tric Kit" Rebuild kits come with one that has no markings whatso ever and are usually a 6.5....so vacc pump and suction cup becomes your buddy...

Optional:
If a dual stage PV the letter and number will have to be cross referenced to find the "stages".

Other trivia:
As of about 5 years ago the "9.5" was dropped from the "picture window" style of PV and now only comes in the the "6 little hole" version...Picture window versions are still available from 10.5, 8.5-2.5....