SumDumbGuy

Ok, everybody seems to have varying opinions on how to decide what size power valve to run. I have a Holley 750 DP that I bought used and currently has a 4.5 power valve.
It's on a freshly build daily driver 355 sbc roughly 10:1 compression. The cam is close to the specs of the 1970 LT1.
Manifold vacuum at idle in gear is 11 inches.
Holley's site says half of manifold vacuum at idle in gear, which would give me a 5.5 PV. I've read on other sites that you should go two sizes below manifold vacuum, which would give me 9.5 or 8.5 PV. The sticky in this forum says probably a 10.5 or 12.5 PV.
The car isn't running perfect so I'd like to figure out the right one so I can pick away at fine tuning everything else. Or should I just buy a stock 6.5 until all the other bugs are out and then mess with different power valves later?

Apeiron

There's a certain amount of driver preference to it. Too low and it'll feel sluggish unless your foot is right into it. Pick a higher value, and you'll feel great throttle response but mileage will suffer.

I'd leave the power valve selection until everything is running smoothly.

SumDumbGuy

Thanks for the input!