Stock 455, 750 double pumper, which power valves do I want?

 

The one it came with

 

try a 4.5

 

Thanks Dave, I'll give it a try. Tripduces doesn't know much about power valves and backfires does he?

 

Take a vac reading @ idle and divide that number by 2 and that's what you'll need

 

Are you asking me or taking a poke at me?
I know a lot about Holleys, backfires and power valves.
There is no reason to go with a different power valve then the one that came on that carb with a stock engine.
How many inches of vacuum are you pulling at idle? What's the lowest vacuum reading you observe while driving normally around town?

"Take a vac reading @ idle and divide that number by 2 and that's what you'll need"

^ this is incorrect yet it seems to be an urban legend nowadays

 

Then call Holley about it and have them change their website. The manufacture of the carb doesn't know what they are talking about then
http://forums.holley.com/entry.php?4...r-Valve-Tuning

 

and that carb was not stock to the car to begin with...

 

"Automatic transmission vehicles need to be in the Drive position, while manual transmission vehicles can be in Neutral."

You neglected this key statement

"and that carb was not stock to the car to begin with..."

What does that have to do with the question asked?

 

Thats why I gave him the link as well, he didn't state if it was auto or stick so I wasn't going to assume. What I do know is the you can take any SAME stock motor and read the vac on 10 of them, and 9 out of 10 will have a different vac readings. So the statement of just throw whats on there would be incorrect. And most rebuild kits come with two PV's to chose from. So to answer the OP's question. Take a vac reading and divide by 2. There is no myth about how a PV works. Gas is supplied through the valve by the pressure its reading. So it's kinda important to know that info when selecting the correct one for your application.

 

He never mentioned anything about rebuild kits. He stated he had a 750 double pumper on a stock 455. That's it.
That means he has either a 6.5 power valve or a 8.5 depending on the model. Once again we don't know that.
What I do know is a stock 455 draws a lot of vacuum and the power valve that came with that carb, whichever it is, will be just fine.
The answer Holley gave on their forum is a very simplistic answer that would satisfy most people but it's not a thorough answer. You need to hook a vacuum gauge to it and run that car around town as you normally would recording the lowest vacuum reading (No WOT) and then go 1.5-2 inches of vacuum lower than that reading on the power valve.
That's the correct way of doing it. For the record RJ, you didn't give a link until you were called out.

 

What makes you think you need something other than what it comes with?
If there weren't any in it then just go to the Holley website. They'll have what should be in there to begin with, power valves, jet sizes, accelerator cam etc. Then go from there.

 

lol You called me out on it so I supplied a link. First one that pop's up on power valves just so happened to be from Holley. Merry Christmas though

 

So which power valve did you end up going with?