Holley Power Valve selection Q
Thread Starter
Instructor
Joined: Nov 2003
Posts: 137
Likes: 5
From: Clifton NJ
Holley Power Valve selection Q
Now that I have the engine work completed, I want to dial in the 650cfm Holley I have. I measured the vac @ idle in drive, and I get 17" Hg. The rule of thumb I recall for selecting the value for the Power Valve was 2" Hg less than the vac reading @ idle, which would indicate a 15" Hg PV. Holley only supplies PVs up to 10.5" Hg. I'm anticipating a lean stumble under acceleration, due to the PV not opening until the vac drops to 10.5"Hg. Any suggestions?
Thanks
BB NJ Ken
Thanks
BB NJ Ken
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
There's plenty to be confused about with PV's,..hell, call Holley, talk to three different techs, get three different answers.
I'd go with the 10.5 and make sure you have a good strong accel. pump shot. Use the brown pump cam if you need to.
The PV would come into play, for instance, if you're cruising the highway, and you encounter a hill,..this is where you need it to open at the right time.
Obviously, it's in play on WOT or heavy acceleration but most any PV will do it's job at WOT with 3-4 inches of vacuum, or less.
Not much help,..am I.
I'd go with the 10.5 and make sure you have a good strong accel. pump shot. Use the brown pump cam if you need to.
The PV would come into play, for instance, if you're cruising the highway, and you encounter a hill,..this is where you need it to open at the right time.
Obviously, it's in play on WOT or heavy acceleration but most any PV will do it's job at WOT with 3-4 inches of vacuum, or less.
Not much help,..am I.
Drifting
Joined: Dec 2004
Posts: 1,345
Likes: 3
You need to measure the vacuum when cruising and subtract 2 ("). It will not richen the mixture at idle at any vacuum level.
If you set it 2" below idle vacuum, it will be richening the mixture virtually ALL the time you are driving!!!
The power valve richens the mixture during throttle transitions, it is not meant to richen whenever you are off idle.
If you set it 2" below idle vacuum, it will be richening the mixture virtually ALL the time you are driving!!!
The power valve richens the mixture during throttle transitions, it is not meant to richen whenever you are off idle.
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
6.5 is the most common power valve opening unless you have a "big" cam then the 2 inches under idle vacuum rule applies as in 6-7 inches of vac at idle would use a 4.5 power valve. if you use a 10.5 power valve the power valve will open too soon killing fuel mileage
Racer
Joined: Apr 2005
Posts: 494
Likes: 0
From: Virginia
Originally Posted by olescarb
6.5 is the most common power valve opening unless you have a "big" cam
