Power valves.

What effect might the 4 door power valves have on jetting? I was doing a little tuning,cleaning, and putting new gaskets in my carb. Decided to change the power valve to match the engines vacuum better. The old one was a high flow 4 door deal. All I had to replace it with was a standard. Might that change much? Also where in the range may it change?

ham fisted carb guys would break the big cutaway pv. To me they work the same.

The openings in the power valve itself should not produce any metering effect. All metering should be done at the PV channel restrictions in the metering block. With that said when running methanol high flow designs are sometimes needed to keep up with the demand for fuel volume at WOT.

what was vac num on old? and on new?

Old was 6.5. New is 8.5. Vacuum in gear 17.5.

It is my understanding that Hi-flow power valves are only for use on metering blocks with large power valve channel restrictions (PVCRs). These metering blocks are only used on large CFM carbs and are designed to be used with metering blocks which have 0.097"-0.128" size PVCRs.

I'm not sure why mine had one. I replaced it with a regular one. Didn't seem to effect the jetting any.

The power valve should be rated at half of what your vacuum reading is at idle.

id install a 6.5 large window valve in it

We use the hi-flow power valves in our alcohol carburetors as well as our E-85 and blow-through stuff but as mentioned the pvcr is what actually controls the anount of fuel for the circuit. For gas the standard power valve is fine and as mentioned typically half of the engines vacuum. From there they can be changed up or down to control when the fuel enriches but is usually best done with a meter.