Power Valve Selection

72bluNblu said
This is true, but the generic estimate of using the idle vacuum helps with putting you in the ball park for the cam you have. If you have a lower idle vacuum than "standard" you will likely need to bump the PV rating down as well. If you have a fairly stock engine than the out of the box 6.5 PV should be close. And then you drive the car and determine where the PV is coming in and adjust from there.

I have a nice uphill section of freeway I use, plus my AFR gauge, to figure out where the PV is coming in. It's a bit easier though for me because I have mechanical secondaries, so, I know the throttle position when those start to come in.

True, their guideline may get someone in the ballpark. I was just pointing out that "selecting" a power valve using an idle vacuum is not the correct method. Sure, it may get you in the ball park, but the actual "selection" and tuning of the proper PV should be based on what the engine wants during certain driving conditions as @Carnut68 (and you) described. Turns out, mine wanted a 10.5 version and could probably benefit from a higher one than that.