How do you select the right power valve?

[19Fordy]

I would like to know how to select the correct single stage AND
two-stage power valve for my Holley 390 4 bbl. carburetor with #51 jets.
My goal is to improve the gas milage as my present carb "gobbles" gas. The engine is a stock 239 cu.in 8BA. I live at sea level elevation. I have been thinking about installing #50 jets also, but I don't want to burn the valves so I began to think about changing the power valve. The engine idles at 17 in.of mercury. Your knowledge and experience is appreciated.

[BUBBAS IGNITION]

Will take some trial error all involving the vacuum gauge. The number of the valve is the vacuum reading that the valve opens allowing for the power circuit to kick in.
Lets say its a #7 (that 7 inches of vacuum) . Drive the car while watching vac gauge , can you feel the power circuit kick in at 7" ? Adjust and change valve until the feel ( and overall performance is perfect.....
Do some googling on how to make the carb perfect........

[Charlie ny]

19,
I sure like Bubbas idea. You might also consider using an air/fuel
gage. Not cheap, Summit has nice ones for about $300. You must
weld a fitting in your exhaust pipe 18 to 24 inches down from the
motor for installation of the o2 sensor. Watch the meter as you drive / pound
your car and you can see by the read out exactly where you are
rich or lean. I fumbled around dialing in my ancient Rochester 4 barrel
and finally got sick of guessing and purchased and installed the A/F
gage. I was surprised at how much more that gage knew about what
was going on in my motor than I did.
Charlie ny

[Ol' Ron]

Charley NY hit the nail on the head here. Richard and I have been using a wide band A/F meter now for several years. The one we have now only goes up to 16:1, we've been looking at one hat goes to 22:1 as our present engine rund in the 16's right now.
As for Power valves, old carburetor designs don't allow changing the AMOUNT of fuel the PV adds to the A/F mix. However the new Edelbrock does. I'm sure othere do to but i'm not familar with them, but Charlet would know.

[flatjack9]

Just be aware that the power valve only turns the extra fuel on, it does not control how much is used. That is controlled by the power channel restriction. I'll try to remember to check my notes tomorrow to see what jets I'm using. My engine is 276 cubes though.

[BUBBAS IGNITION]

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Originally Posted by Ol' Ron

Charley NY hit the nail on the head here. Richard and I have been using a wide band A/F meter now for several years. The one we have now only goes up to 16:1, we've been looking at one hat goes to 22:1 as our present engine rund in the 16's right now.
As for Power valves, old carburetor designs don't allow changing the AMOUNT of fuel the PV adds to the A/F mix. However the new Edelbrock does. I'm sure othere do to but i'm not familar with them, but Charlet would know.

Good discussion here Ron, my experience in emissions etc over the years has shown a 16 to 1 would be way on the lean side. Many shops use a 5 gas analyzer with nox being the latest 5th gas . NOX is created by a lean mixture as well as heat. Some late models are running a 17-18 to one ratio trying to get that last mpg.
Its always a trade off between actual power and fuel economy .

[Ol' Ron]

I realize that Jim, and running to lean can cause other problems as well. So far the 16.?? is working fine. I'd like to get into the 17-18 with the new spark plug location. The new gas has ne worried as well. But if you don't try things like this ya don't learn nuttin.

[BUBBAS IGNITION]

The "new gas" is becoming a situation around here as USAC just announced that they would run a new fuel "green 15 or ethanhol " and make it mandatory that all the silver crown sprint cars run theis fuel as well as the midgets etc.
They supply the fuel at each race event so as to all cars running the same fuel.

Switching from methanol to the new fuel causes quite a bit of injection adjustment and will cost a few bucks per car......

I guess i have become about as "anti green fuel" as i can be !!!!!