Power Valve Selection

RustyRatRod said

The PV comes in "after that" no matter what. You must have air flow across the boosters to pull fuel from the PV and there's nowhere near enough at idle to make it happen. I'm not arguing the point, just saying there's more than one way to tune for a PV.

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And if you need alcohol PV’s in a gas application there’s nothing other to say than that’s not right.

I’m not suggesting that the PV works at idle. Using that calculation is just a way to estimate the PV value in a way that’s tied to the cam that’s in the engine. And that method works pretty well as a ballpark, which is why it’s literally the way that Holley suggests it be done. Bigger cam = less vacuum at idle= lower PV value. Not because the PV has anything to do with idle, but because of what a cam with that profile will do the rest of the time.

The whole point of the PV is to allow for smaller jets so you can get better economy at cruise but then have the PV open under heavier loads. If your PV is open at cruise, it completely defeats the purpose. Just take out the power valve and run larger jets if the PV will almost always be open, like it will be if you’ve got a 12.5 in there.

I’ve run with 6.5, 5.5, and 4.5 power valves in my Duster, can watch when it comes in on my A/F gauge, and the 5.5 works best. Even the off the shelf 6.5 was opening too early.