Jets and Power Valves 750 Holley 4150

AJ/FormS said

run a PV a tad under your cruise vacuum regardless of idle vacuum

Click to expand...

Mostly that would be on engines that are inefficient at part throttle.

mbaird said

agree... but he is asking about his initial setup. So the 1/2 idle vacuum is a easy starting point.

Click to expand...

Seems reasonable.
The situation where it gets people in trouble is engines with very poor idle characteristics. An engine that idles with 5 "Hg, very well might need a PV that opens at 6 or 8"Hg or there will be a flat spot in part throttle acceleration.