Holley Power Valve?

[turbo2256b]

A power valve helps response ,, it also richens the idle circuit , some don't believe it ,, it does , not up for an argument

oNLY Richins THE IDLE CIRCUIT if the power valve is leaking or picking one with an incorrect opening vacuum point.

[sc2dave]

A power valve helps response ,, it also richens the idle circuit , some don't believe it ,, it does

HAHAHAHA

[cjperformance]

And opening the back left door will make the front right tyre go flat !
As said- the power valve value OR wether one is fitted or not has NO affect on the idle circuit whatsoever in a properly working/tuned carb.

[levisnteeshirt]

Your wrong . so wrong . tell us how it feels

[Tuner]

A power valve helps response ,, it also richens the idle circuit , some don't believe it ,, it does , not up for an argument

IF the carb is set up and working correctly it will not have any affect on idle AFR. The video below is a 750, one of a pair set up for external boost referenced on the primary and secondary PV's. The video CLEARLY shows the O2 readings are unaffected when opening or closing the PV at idle. A test was also done at a higher RPM when the boosters were active and O2's are affected as the PV is intended to operate.

https://www.youtube.com/watch?v=jlp-Q_3 ... e=youtu.be

Your wrong . so wrong . tell us how it feels

Did you pull your head out of the sand long enough to watch Mark's video? I guess not.

[prairiehotrodder]

on the power valve topic. I watched the video. I didn't know that. Very interesting. I have another question :

On any given engine no matter what the vacuum. Selecting a lower number PV (2.5 , 3.5 etc...) will that have the effect of slightly delaying the fuel from the PVRC jets? When going to WOT ?

Brian

[cjperformance]

on the power valve topic. I watched the video. I didn't know that. Very interesting. I have another question :

On any given engine no matter what the vacuum. Selecting a lower number PV (2.5 , 3.5 etc...) will that have the effect of slightly delaying the fuel from the PVRC jets? When going to WOT ?

Brian

Correct , the lower the pv number the longer the delay until pvcr's flow fuel. But on the flip side, if you have a small carb and pull much vac at WOT it is possible to begin to pull the pv closed! This effect can also occur on a dp carb lime a 750 holley when too low a # pv is in the primaries, with low gears and when applying the throttle slowly just before opening the secondaries you can pull the pv shut and get a stumble/miss which go's just as the secondaries crack open (and drop the vac) and some people go mad trying to find the problem, use a vac gauge to jet and pv correctly and problem solved!

[MadBill]

<EDIT> Written before seeing above post.

Yes. (unless it's a stomp to WOT, in which case it won't matter.) It's especially evident if you've leaned out the part-throttle cruise. A good example is my pal's 455 Buick Skylark. We jetted the 800 spread bore Holley's primaries down to just above the point of lean surge (~ 10 sizes, AIR) then drilled the P.V.C.R.s to get back to the desired WOT mixture.

It drove like crap! Tipping-in the throttle initially gave no response at all ('stretchiness'), then an actual sag and finally full power. The fix was to go from a 4.5" PV to an 8.5", which eliminated the transient lean-out condition.

[Tuner]

Absolutely. ^^^ what he (they) said ^^^^ the low number PV's will pull closed not open fully. In these modern days when most everybody who is interested in this kind of thing has a WBO2 and a vacuum gauge, I don't understand why we have to keep on plowing this same old tired ground.

If you have to open the throttle so far to get the PV open that there is a range of throttle that should have enrichment, but the valve is closed, eh .... to lean... so sorry.

In the RPM range where the engine is run for racing, the intake vacuum acts more like a stock engine at low RPM. In other words, at high RPM, the intake vacuum will be much higher than at low RPM and idle.

When you are opening the throttle in the race RPM range, a 500 HP engine at 4000 RPM might have 8" vacuum and be making 350 HP, so the PV should be open. If you are waiting for the vacuum to drop from 10" to 2.5" there is a big lean area in the pedal travel. Ask anybody who runs restricted 2bbl engines on a dyno. An average iron head circle track SBC with a 350 2bbl makes about 350 HP at 10" Hg.

The point is, with sporty and radical cams, at racing speed and at highway speed, the intake vacuum is much higher than at idle. Idle vacuum has nothing whatsoever to do with choosing a power valve.

Choose the PV by observing the vacuum characteristics when transitioning from less to more load in the RPM range where useful power is produced.

The idle has nothing to do with it.

[statsystems]

Absolutely. ^^^ what he (they) said ^^^^ the low number PV's will pull closed not open fully. In these modern days when most everybody who is interested in this kind of thing has a WBO2 and a vacuum gauge, I don't understand why we have to keep on plowing this same old tired ground.

If you have to open the throttle so far to get the PV open that there is a range of throttle that should have enrichment, but the valve is closed, eh .... to lean... so sorry.

In the RPM range where the engine is run for racing, the intake vacuum acts more like a stock engine at low RPM. In other words, at high RPM, the intake vacuum will be much higher than at low RPM and idle.

When you are opening the throttle in the race RPM range, a 500 HP engine at 4000 RPM might have 8" vacuum and be making 350 HP, so the PV should be open. If you are waiting for the vacuum to drop from 10" to 2.5" there is a big lean area in the pedal travel. Ask anybody who runs restricted 2bbl engines on a dyno. An average iron head circle track SBC with a 350 2bbl makes about 350 HP at 10" Hg.

The point is, with sporty and radical cams, at racing speed and at highway speed, the intake vacuum is much higher than at idle. Idle vacuum has nothing whatsoever to do with choosing a power valve.

Choose the PV by observing the vacuum characteristics when transitioning from less to more load in the RPM range where useful power is produced.

The idle has nothing to do with it.

So true. But why does everyone think idle vacuum is where you set the PV opening? Who started that? I learned in the early 1980's with 4.56 gears on the street and a cam that had 7-8 inches of vacuum at idle you either had to make it dead rich to live with the cruise using a PV that has a less than idle opening, or, you could measure vacuum at cruise and set it for that.

IMHO, I think the damned thing is named wrong. If it was called an economizer valve it would help understanding how it functions. I'm sure at a 3500 RPM cruise most engines have will have an incredible amount of vacuum. I'm at about 13 inches and run a 10.5 PV.

[cjperformance]

Anyone who has studied the fuel flow path thru the main, pv , idle and trans circuits in a carb AND can also tune the idle circuit to work correctly know (or should!) how the pv works. Also anyone willing to listen, learn and experiment will also realise this.
Its unfortunately people who have a mismatched combo and no idea how to tune a carb that rely on bandaid fixes that spread such nonsense!

[jmarkaudio]

A power valve helps response ,, it also richens the idle circuit , some don't believe it ,, it does , not up for an argument

IF the carb is set up and working correctly it will not have any affect on idle AFR. The video below is a 750, one of a pair set up for external boost referenced on the primary and secondary PV's. The video CLEARLY shows the O2 readings are unaffected when opening or closing the PV at idle. A test was also done at a higher RPM when the boosters were active and O2's are affected as the PV is intended to operate.

https://www.youtube.com/watch?v=jlp-Q_3 ... e=youtu.be

Your wrong . so wrong . tell us how it feels

Did you pull your head out of the sand long enough to watch Mark's video? I guess not.

Stuck in quicksand. And the more you fight it the deeper you go...

[Walter R. Malik]

I think the misconception comes from a lot of people not realizing that their carburetor throttle plates are probably open far enough at idle to allow some slight fuel mist, which is not easily visible, to be expelling from the booster ... which will add some fuel at idle.

In cases such as that ... the power valve being open CAN affect the idle mixture.
The issue there is not the power valve itself but, with the excess throttle opening having an effect upon the booster.

[cjperformance]

I think the misconception comes from a lot of people not realizing that their carburetor throttle plates are probably open far enough at idle to allow some slight fuel mist, which is not easily visible, to be expelling from the booster ... which will add some fuel at idle.

In cases such as that ... the power valve being open CAN affect the idle mixture.
The issue there is not the power valve itself but, with the excess throttle opening having an effect upon the booster.

Yes most definetly. And a real easy way to see such fuel if its suspected this may be happening is to look down the top of the carb using a connected timing light (or any strobe light), any fuel exiting the boosters is very easy to see this way , without the strobe effect a small ammount of fuel may go unseen.

[levisnteeshirt]

Go on , keep putting out bad info , and while your at it , keep moving the IFR to the bottom ,, i especially love that one , , if you dont know what something does , you really shouldn't comment on it ,, earth to air heads , not every carb is built to run on a delay box held wide open against a brake ,, there is circle track , and real street carbs that benefit from making a holley carb work in every facet of its capacity to give the engine what it needs at any time , ,, if you cant see that more head pressure on the main well is going to increase idle fuel ,, you really have no clue what your doing , or just stick to dynos and transbrakes