View Full Version : Holley Power Valves

29-08-02, 10:28 AM
Can anyone tell me the best way to select the correct power valve in my Holley Street Avenger 770 vacuum secondary carb.

Engine is a 400ci Chevy smallblock with Dart Pro 1 aluminium heads, 10:1 C.R., Edelbrock Performer RPM dual plane inlet, MSD 6AL ignition, Crower hydraulic roller cam. On the dyno it made 413bhp & 503lbft torque.

I hooked up a vacuum guage and drove it around. Idle vacuum is approx. 14mg and cruising vacuum is a steady 17/18mg.

What am I looking for or is it a question of feel?

As I understand it, you want the power valve to stay shut when cruising but it to open when you nail it?


29-08-02, 01:19 PM
Simon - I am no expert on Holleys, but as far as I can remeber, the starting point for rating power valves is 50% of tickover vacuum.

BTW - I don't understand the units you have used for your vacuum readings? Usually expressed as inches of waterguage.