Re: Holley power valve identification
I can't believe Holley would spread a myth like "half the vacuum at idle" for a power valve. Bull. If you have an air/fuel meter and a vacuum gage you can find the exact valve needed. Put in a really low power valve like a 3.5". Go up a hill in high gear (to put a load on the motor) and hold the vacuum at 8" and watch the air/fuel meter. Then hold it at 7", then 6", etc. When the motor leans out (you'll feel it surging at that point even if you don't have an air/fuel meter) look at the vacuum gage and pick a power valve 1-2" higher. I can make my idle vacuum change 5" just by turning the idle speed screw. What does that have to do with the power valve? You need to find the point where the motor needs to transition from the 'cruise' mode mixture to the 'power' mode mixture. A heavy vehicle needs to transition sooner than a light vehicle. 2.56 gears need to transition sooner than 5.13 gears. Some high overlap cams idle at 5" but cruise at 15" and need 8.5" power valves. Put a 2.5" valve in there and watch the motor rattle the bearings out going up a hill at 6" vacuum. The motor tells you what it needs. Argue with it and see who wins.