I'm currently running a 670 Holley Street Avenger on a 327 with a .480 lift cam and getting 10 inches vacuum. It has a 6.5 power valve in it. Would it be better to put a 4.5 power valve in it?
You are really the only one that can answer that. A power valve OPENS when vacuum falls BELOW it's set point, say 6.5, and enrichens the whole deal. Put a vacuum guage on you car and drive around a bit and see where your vacuum numbers go. It's best set up so your power valve is closed at steady state cruise but opens at acceleration.
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