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Hi all I have a doubt about my 4777 holley carburetor. I'm rebuilding it but I'm not sure about which power valve to use.
This is the original one (6.5hg): Original power valve 6.5hg
And these are the valves provided with the kit: Holley rebuild kit power valves
I want to use one of the two 6.5hg but which one?
On the first is stamped the number 23418. And in the other 31318. What these numbers means?
Probably date codes, you can check these with a hand vac. pump to see how close to the rated (6.5") vac. the valve actually opens at. I've only seen them off if they are really old and the rubber has gotten stiffer.
Figuring out what opening point you should actually have is more complicated and depends on Cam, Trans. type, R/E ratio, car weight etc.
If you have a an AFR meter/data logger it's pretty easy to dial in the PV opening value.
Holley usually gets you pretty close on the aftermarket Carbs as long as you picked the correct CFM size.
From: At my Bar drinking and wrenching in Lafayette Colorado
The 6.5" Power Valve is a good, generic PV for most mild performance applications. Many of the factory-installed Holleys used 8.5 Power Valves due to the relatively mild factory cams. If you'd like to dial it in a little closer for your specific engine, you can hook up a vacuum gauge and note the vacuum reading on your engine (with the transmission in "drive" if it's an automatic). Divide the reading by 2 to get a power valve setting that will be pretty close for your application. I'm running a big solid roller cam in my 407, and I pull about 11-12 inches of vacuum at idle. I use a 5.5 PV, and it works perfectly.
Holley power valve
