Racing Fuel Systems

Hello, I’m trying to select a power valve for my Holley 750 double pumper. I’m at the point where I have the transfer slot exposure set and I closed the primary idle speed screw and opened the secondary idle speed screw to keep the same idle speed. I leaned the primary main jets until it surged in 4th gear going up a slight hill and cruising on the highway. I went up 2 jet sizes once I got it to surge. I heard that you can plug the PV, take it out for a cruise, slowly get into the throttle and see at what vacuum it feels like it starts to surge. My question is that when should I be looking for it to surge? On the highway in high gear with light throttle or high gear going up a slight hill? Or just driving regularly in any gear? I currently have a 8.5 but I’m just trying to determine if the carb needs more or less. Thanks.

So if it surges when I open the throttle more at cruise at let’s say at 8” of vacuum then I would need a 8.5” power valve correct? The trickiest part is figuring out how I can route the vacuum house from the engine to inside the car because I don’t have any open holes in my firewall so it’ll have to be routed outside of the car.

Personally I have never heard of this method of choosing a power valve. Can you define " surging "? Hesitation , trailer hitching ?
I assume you are not having any issues that you are trying to correct. Some people take the cruise vacuum reading , divide the reading in half to choose the power valve. Example , cruise vacuum is 18" divided by 2 is 9. So 8.5 power valve would be acceptable.

6.5 is the standard Holley power valve. Millions of them running around with that and doing fine. Vacuum at idle has nothing to do with power valve decision. Surge can also be a timing issue.

Jmarkaudio on a yellowbullet forum said “ I would plug the PV, take it out for a cruise, slowly get into the throttle and see at what vacuum it feels like it starts to surge. Or if you want to just throw a safe one in use an 8.5.”

I have always thought to drive the car at 45 55 65 mph and note the lowest cruise vacuum then select a valve opening point approx 2" lower, the goal being that no power enrichment under low load cruise conditions.