rear power valve on HP holley should i run one ?

[shoedoos]

Is this what you're looking for?

https://www.ebay.com/itm/Garage-Sale-An ... Swe7pegPsM

[MadBill]

Well done!
BTW, Speedway has the same pic: https://www.speedwaymotors.com/Garage-S ... 49860.html

[Walter R. Malik]

hi fellas ive noticed on my HP holley it has a rear power valve, i thought it was a little strange as ive never run one on the rear before, is it a good thing or bad ? im thinking it would suffer from fuel slosh under acceleration. what do you guys think? thanks.

A secondary power valve on a Holley type carb is there so, the secondary main jetting can remain smaller to help keep fuel from running out of the rear boosters during deceleration or high G side to side movement.

A drag engine doesn't really need one however, just about any other scenario can usually benefit from having one.

[rfoll]

I tried running a power valve secondary on an 4781 and it bogged terrible at the track. It didn't show up on the street because the tires were already spinning before I got to wot. I suspected the power valve took too long to open and feed fuel.

[ClassAct]

Well done!
BTW, Speedway has the same pic: https://www.speedwaymotors.com/Garage-S ... 49860.html

How does that thing work? Does it snap over the power valve and hold fuel around it?

[MadBill]

Yes.

[levisnteeshirt]

I tried running a power valve secondary on an 4781 and it bogged terrible at the track. It didn't show up on the street because the tires were already spinning before I got to wot. I suspected the power valve took too long to open and feed fuel.

It has to be sized correctly and jetting adjusted ,, this allows the idle on the secondary side to be leaner since it's fed from the main well which is fed from the main jet ,,, it usually enhances throttle response greatly if done correctly ,, comp products sells a cap also for drag racing

[novadude]

I tried running a power valve secondary on an 4781 and it bogged terrible at the track. It didn't show up on the street because the tires were already spinning before I got to wot. I suspected the power valve took too long to open and feed fuel.

It has to be sized correctly and jetting adjusted ,, this allows the idle on the secondary side to be leaner since it's fed from the main well which is fed from the main jet ,,, it usually enhances throttle response greatly if done correctly ,, comp products sells a cap also for drag racing

I'm confused as to why the power valve would have anything to do with the secondary idle? Secondary metering blocks have an IFR that is going to be smaller than the secondary main jet whether or not a secondary PV is used. Since the secondary IFR will always be smaller, I can't see how secondary main jetting would have any impact on the secondary idle circuit.

[GRTfast]

I tried running a power valve secondary on an 4781 and it bogged terrible at the track. It didn't show up on the street because the tires were already spinning before I got to wot. I suspected the power valve took too long to open and feed fuel.

It has to be sized correctly and jetting adjusted ,, this allows the idle on the secondary side to be leaner since it's fed from the main well which is fed from the main jet ,,, it usually enhances throttle response greatly if done correctly ,, comp products sells a cap also for drag racing

I'm confused as to why the power valve would have anything to do with the secondary idle? Secondary metering blocks have an IFR that is going to be smaller than the secondary main jet whether or not a secondary PV is used. Since the secondary IFR will always be smaller, I can't see how secondary main jetting would have any impact on the secondary idle circuit.

I have verified through testing that the main jet has nothing to do with idle mixture for the exact reasons you described. At least least for a Holley style carb anyway.

[rfoll]

I tried running a power valve secondary on an 4781 and it bogged terrible at the track. It didn't show up on the street because the tires were already spinning before I got to wot. I suspected the power valve took too long to open and feed fuel.

It has to be sized correctly and jetting adjusted ,, this allows the idle on the secondary side to be leaner since it's fed from the main well which is fed from the main jet ,,, it usually enhances throttle response greatly if done correctly ,, comp products sells a cap also for drag racing

The power valve and jettng was factory correct, and I put larger jets in both sides to account for the big cam and headers. The afr was going to full lean until the engine recovered from the bog. I put my 780 on and decided to fight with it another day

[levisnteeshirt]

What was the diameter of the hole behind the power valve ? Adjusting for a large cam and headers is iffy ,, it's airflow sensitive , and idle vacuum sensitive ,, I'm always a wait and see what it likes before I make a change myself

[RTR-1]

I know BLP and possibly other billet blocks have the power valve channels located lower. That will help to prevent picking up air on the secondary side, especially when used with a cap.

[MadBill]

... comp products sells a cap also for drag racing

So they do: https://www.competitionproducts.com/Weg ... rdqxkRKiUk

BUT it's 3X what Speedway wants for one!

[ClassAct]

... comp products sells a cap also for drag racing

So they do: https://www.competitionproducts.com/Weg ... rdqxkRKiUk

BUT it's 3X what Speedway wants for one!

I think the one above has that plastic extension where the Speedway Motors doesn’t have that, so maybe that’s why its a bit more...but 3x’s more it better come highly polished.

I’m following this thread because I want to use 1:1 linkage and square jetting on both ends so I can cruise on the transfer slots longer, if that makes sense.

[MadBill]

...I think the one above has that plastic extension where the Speedway Motors doesn’t have that, so maybe that’s why its a bit more...but 3x’s more it better come highly polished...

That looks like the vent whistle that most HP metering bodies include. Another cap is in the lower right of the pic.