Holley rebuild

[Axel 427]

I got my self into a pickle. I torn down my Holley 670 with vac.secondary. I didn't pay attention which power valve I took off the front and back. The stamped numbers are different. One valve says either 589 or 586 and the other says 451.
The rebuild build kit came with 3 valves, 6.5, 10.5 and a 2.5. Any advice with be greatly appreciated.


Vance

[jetblue69]

Originally Posted by Axel 427

I got my self into a pickle. I torn down my Holley 670 with vac.secondary. I didn't pay attention which power valve I took off the front and back. The stamped numbers are different. One valve says either 589 or 586 and the other says 451.
The rebuild build kit came with 3 valves, 6.5, 10.5 and a 2.5. Any advice with be greatly appreciated.


Vance

Well, stock should be a 6.5... But, if you have a somewhat healthy cam that's not going to be the one you want. More cam = lower number power valve. On a naturally aspirated engine of course. Vacuum at idle (full vacuum, not metered) divide by two and if it's a whole number pick the power valve with the next LOWER half number.

Of course the ideal way is with a vacuum gauge and a air/fuel meter but that methodology will get you in a really nice ballpark. I've done it the old school ways for years and it always worked for me but I'm sure some of the internet commandos on here will try to sell you the Brooklyn Bridge.

[moore_rb]

Holley power valves are typically stamped based on how much vacuum is required to open them, but I've never seen one stamped with 3 numbers - Usually there is one letter, and 2 numbers.

Based on that, I suspect that the one you have stamped 451 is probably actually an "I-4-5" - If I'm correct about this, then that one would be set to open at 4.5 inches of mercury, and would go with your secondary metering plate.

For the other one- Are you sure the "8" isn't a "G"? I guessing that it might be a "G-6-5", which would open at 6.5 inches of Mercury, and would go on your Primary metering plate. I doubt the 6 is a 9, but even if it is, 9.5 is still a higher number than 4.5, and so it would still go on the Primary metering plate.

When your power valves are 2 different sizes on a vacuum secondary carb, the higher value power valve typically goes on the primaries, so it will open first as vacuum falls under hard acceleration, as a general rule.

[Axel 427]

Originally Posted by jetblue69

Well, stock should be a 6.5... But, if you have a somewhat healthy cam that's not going to be the one you want. More cam = lower number power valve. On a naturally aspirated engine of course. Vacuum at idle (full vacuum, not metered) divide by two and if it's a whole number pick the power valve with the next LOWER half number.

Of course the ideal way is with a vacuum gauge and a air/fuel meter but that methodology will get you in a really nice ballpark. I've done it the old school ways for years and it always worked for me but I'm sure some of the internet commandos on here will try to sell you the Brooklyn Bridge.

So what would you suggest. I have 3 new valves, 2.5, 6.5, 10.5 that came with the kit. I'm not sure of the cam. It's on a S/B 427 Roush R .

[Axel 427]

Originally Posted by moore_rb

Holley power valves are typically stamped based on how much vacuum is required to open them, but I've never seen one stamped with 3 numbers - Usually there is one letter, and 2 numbers.

Based on that, I suspect that the one you have stamped 451 is probably actually an "I-4-5" - If I'm correct about this, then that one would be set to open at 4.5 inches of mercury, and would go with your secondary metering plate.

For the other one- Are you sure the "8" isn't a "G"? I guessing that it might be a "G-6-5", which would open at 6.5 inches of Mercury, and would go on your Primary metering plate. I doubt the 6 is a 9, but even if it is, 9.5 is still a higher number than 4.5, and so it would still go on the Primary metering plate.



When your power valves are 2 different sizes on a vacuum secondary carb, the higher value power valve typically goes on the primaries, so it will open first as vacuum falls under hard acceleration, as a general rule.

Yes sir....your probably right. The numbers are hard to read, plus my eye sight going to crap.

[DanEC]

Do you know what you engine vacuum at idle is?

Choosing the Right Power Valve for Your Holley Carburetor – RacingJunk News