Holley 401, Tuning For WOT

[TC]

I've always been under the impression that if you need to richen up or lean out the WOT mixture that you just change the main jets in the appropriate direction to achieve the AFR that you want...... But in the book I'm reading Vizard says the proper way to adjust WOT is to tune the "Power Valve Channel Restrictor(PVCR)"..... Basically saying that you tune all part throttle tuning using the main jets and once you get that dialed in you tune the PVCR to achieve the desired WOT AFR's......

Question is has anyone ever tuned a carb this way and is there really that big of an advantage to tuning the PVCR over just changing the main jets??.....

[Scott Liggett]

Not sure what a Holley 401 is, but here goes.

The main jets are for cruising and part throttle. Tune them in that capacity of driving. Don't forget that your idle circuit is part of the main circuit. An AFR gauge is the best thing for tuning part throttle and cruising throttle.

WOT, is the secondary system. The jets, the power valve(s), and the secondary accellerator pump on double pumpers. The power valve opens at a specific vacuum range, the rear jets start moving fuel when the throttle is opened past a certain point.

The power valve opening is the equivalent of about nine or ten jets. Your secondary jetting should take this into mind. The power valve jetting is static unless you want to drill out the restrictor holes. I wouldn't. I would tune the WOT with the secondary jetting.

[MR P-BODY]

For WOT.... I change jets(no PV ) both pri and second..
I try to keep them squared up

[TC]

For WOT.... I change jets(no PV ) both pri and second..
I try to keep them squared up

It's not the Power Valve(s) themselves that he's talking about, he's talking about the channel in the metering block that supplies the added fuel to the booster when the power valve is open...... Basically after you tune for part throttle driving if your WOT AFR's would be to lean, you would end up drilling the Channel in the metering block to a larger size to richen it up......

[TC]

Not sure what a Holley 401 is, but here goes.

The main jets are for cruising and part throttle. Tune them in that capacity of driving. Don't forget that your idle circuit is part of the main circuit. An AFR gauge is the best thing for tuning part throttle and cruising throttle.

WOT, is the secondary system. The jets, the power valve(s), and the secondary accellerator pump on double pumpers. The power valve opens at a specific vacuum range, the rear jets start moving fuel when the throttle is opened past a certain point.

The power valve opening is the equivalent of about nine or ten jets. Your secondary jetting should take this into mind. The power valve jetting is static unless you want to drill out the restrictor holes. I wouldn't. I would tune the WOT with the secondary jetting.

You know like English 101, this is Holley 401 for the advanced tuner....

[MR P-BODY]

It's not the Power Valve(s) themselves that he's talking about, he's talking about the channel in the metering block that supplies the added fuel to the booster when the power valve is open...... Basically after you tune for part throttle driving if your WOT AFR's would be to lean, you would end up drilling the Channel in the metering block to a larger size to richen it up......

I was saying I dont run PVs.. thats why I said(no PV)

[JeffMcKC]

IF,,,, you run PVs then yes. Thats a common way, thats why you dont want the vaccum to raise up and close the PV. It will lean out and kill the engine.

[PatricksDad]

IF,,,, you run PVs then yes. Thats a common way, thats why you dont want the vaccum to raise up and close the PV. It will lean out and kill the engine.

So if I'm a bracket racer, and I'm feathering it through the lights at 6 grand to keep from breaking out, would that be long enough to do damage?

[JeffMcKC]

If it is, you will see it on the plug first. Most guys dont run bracket engines so border line, they stay more consistant.

[MR P-BODY]

So if I'm a bracket racer, and I'm feathering it through the lights at 6 grand to keep from breaking out, would that be long enough to do damage?

If you are a bracket racer and really sand bagged on the dial in... that
would give you more time at part /less than full throttle it could hurt the
engine driving it way lean... this is more so in the late fall when the temps
drop off and your needing more fuel... it doesnt take long to hurt a engine
thats running lean... I dont run PVs in the race car.. they only help when
driving in the pits, thats the only part throttle driving I do with that car