Selecting power valve method Holley 4160

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Slantsix64

Slantsix64

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Hey guys I been reading up on Holley seems like there’s two ways to select a power valve, which one do you guys use?

In gear warmed up I am at 15 inches of mercury and cruising light throttle I am at 22 inch or mercury
 
The best way to pick a power valve is to watch a vacuum gauge that you temporarily hang in the cabin while driving. That way you can tell exactly when you want the extra fuel to come in. I would guess you will end up with a 10.5 - 12.5 with as much vac as your engine has.
 
Post #4 for the win!
Install a PV plug and go drive it. Watch the gauge, as you do some gentle roll-ons. Correlate the power-sag to the gauge. then
Install whatever it points to; as @hunt2elk says probably up around 10.5 or more.
If you have been running a 7.5PV or less, you will find that now, with the right PV, ON THE STREET, you can probably reduce your MJ one size for everything but WOT.
To get the WOT fuel back just increase your secondary the one size.
If you were running a 6 number stagger, just try an 8 number.

When I installed the 10.5 in my 367, with the 223/230/110 Hughes cam, Drivability was much smoother and, had I had a 12.5, I would have tried it. As it was, the 10.5 felt pretty good so I left it
Going from memory, (this was in 2001), with the 10.5;
the P-jets went from 70>72, to 68>70, and it ran well on the 70s.
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When I installed a fresh above-the-hood air intake, and a 230/236/110 Hughes cam,(2004) the Primaries were lean at 68, not bad at 70, maybe a hair off at 72, and fat at 74 with an 8 number secondary stagger; so I ran it at 72P/78S for a long time, and eventually it settled at 74/80. But
On the street, I like to run a lil lean, 72/78>80 cuz it's snappier, and still revs happily to 7200.
The truth is that from 25/30 mph, to 65 mph, at WOT, is like less than 3 seconds, and my combo likes it a hair lean, (exploding in tire-smoke, fury, and a raucus roar that attracts cops like bees to flowers), so, she's not particularly fussy about the perfect jet-sizes, cuz the engine is not working hard at all..
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BTW, congratulations on selecting a sweet 9.5Scr/264 cam combo. In the 318, the Wallace calculator predicts a cylinder pressure of around 155psi@900ft elevation, which should still be able to run 87 gas; and it predicts a V/P of 120, which is pretty good for a cammed-up 318.
This V/P ratio, is over 8% better than than a stock lo-compression version; and only 10% sacrifice to a stock 9.0 engine; So you split it pretty good.
 
AJ/FormS said:
Post #4 for the win!
Install a PV plug and go drive it. Watch the gauge, as you do some gentle roll-ons. Correlate the power-sag to the gauge. then
Install whatever it points to; as @hunt2elk says probably up around 10.5 or more.
If you have been running a 7.5PV or less, you will find that now, with the right PV, ON THE STREET, you can probably reduce your MJ one size for everything but WOT.
To get the WOT fuel back just increase your secondary the one size.
If you were running a 6 number stagger, just try an 8 number.

When I installed the 10.5 in my 367, with the 223/230/110 Hughes cam, Drivability was much smoother and, had I had a 12.5, I would have tried it. As it was, the 10.5 felt pretty good so I left it
Going from memory, (this was in 2001), with the 10.5;
the P-jets went from 70>72, to 68>70, and it ran well on the 70s.
____________________________________________________________
When I installed a fresh above-the-hood air intake, and a 230/236/110 Hughes cam,(2004) the Primaries were lean at 68, not bad at 70, maybe a hair off at 72, and fat at 74 with an 8 number secondary stagger; so I ran it at 72P/78S for a long time, and eventually it settled at 74/80. But
On the street, I like to run a lil lean, 72/78>80 cuz it's snappier, and still revs happily to 7200.
The truth is that from 25/30 mph, to 65 mph, at WOT, is like less than 3 seconds, and my combo likes it a hair lean, (exploding in tire-smoke, fury, and a raucus roar that attracts cops like bees to flowers), so, she's not particularly fussy about the perfect jet-sizes, cuz the engine is not working hard at all..
__________________________________________________________________

BTW, congratulations on selecting a sweet 9.5Scr/264 cam combo. In the 318, the Wallace calculator predicts a cylinder pressure of around 155psi@900ft elevation, which should still be able to run 87 gas; and it predicts a V/P of 120, which is pretty good for a cammed-up 318.
This V/P ratio, is over 8% better than than a stock lo-compression version; and only 10% sacrifice to a stock 9.0 engine; So you split it pretty good.
Click to expand...
Thanks AJ yes this Cam combo I have is really great, the next thing I would do to it is add 1.7 rockers since I already have the magnum heads! Boost my lift and keep the duration the same would probably run good with my 3k stall
 
With a 3000 stall, the PV-calibration won't hardly matter.
As to 1.7 rockers; IMO, at this power level, they're not gonna do much for ya. If I had them, sure, I'd be tempted to install them, but I sure wouldn't rush out and buy them.
Sounds like a fun combo.
 
Slantsix64 said:
Hey guys I been reading up on Holley seems like there’s two ways to select a power valve, which one do you guys use?

In gear warmed up I am at 15 inches of mercury and cruising light throttle I am at 22 inch or mercury
Click to expand...

Neither one is really correct.
The second one is closer to the functional reason for enrichment.

Enrichment is needed under heavy load.
Manifold vacuum is a good indicator of load.

Do I hear you ask: How heavy? How does that translate to manifold vacuum?

It depends on the engine. An engine that is more efficient at part-throttle, and has good part throttle fuel distribution, needs enrichment only close to full throttle. For this sort of engine, full enrichment may not be needed until 4 to 6 in-Hg. An engine that doesn't have those characteristics, or maybe is used to pull very heavy loads, will need enrichment sooner. Chevy's 1965 396 used Holley 3310 that came with 10.5 (& 8.5 secondary) PV. Chrysler Hemi with Holley had a 8.5 PV. Those should give you some idea of the ranges that a hopped up engine may want.

If you are already driving the car around, and have a vacuum gage, then see if you notice any flat spots or delays in acceleration as you increase the throttle. If its at consistant vacuum, thats a clue the PV is not enriching at the correct load. You get fancier and more scientific - all depends on how much work you want to put into it.

One other important point. More timing for lean conditions. When the engine wants enrichment, it also will then need less vacuum advance. There should be no vacuum advance at full enrichment. These two things work together.
 
My answer is, whichever way your engine runs and responds best. Just experiment around with it. No one way will result in the best results for everything. Anyone who tells you that is an armchair tuner. I've actually DONE it. My truck runs best using idle vacuum. Vixen runs best using cruise vacuum. I've tried both ways on both vehicles. I think the reason the truck runs better using idle vacuum is because of its heavy weight.
 
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www.forabodiesonly.com

Power Valve Selection: The Definitive Answer

There are varying opinions on how one goes about selecting a power valve for Holley based carbs (as anyone who has worked on one well knows) There's the 1/2 of idle vacuum, either with 4-speed in neutral or auto in drive, the more widely accepted 2" less than cruise vacuum, I've also seen people...
www.forabodiesonly.com www.forabodiesonly.com
 
AJ/FormS said:
With a 3000 stall, the PV-calibration won't hardly matter.
As to 1.7 rockers; IMO, at this power level, they're not gonna do much for ya. If I had them, sure, I'd be tempted to install them, but I sure wouldn't rush out and buy them.
Sounds like a fun combo.
Click to expand...

A converter will affect power valve timing??

That’s dead wrong.
 
If I have a 3k stall wouldn’t I want to have enrichment from the power valve sooner vs later @AJ/FormS ?

Thanks for everyone’s replies! I really do appreciate everyone’s input and personal opinions

I just installed the 10.5 power valve and wow, really responsive off the line at WOT, but I had a little hesitation at WOT so I tightened up my quick fuel adjustable secondary pot to have the secondaries come in later and the hesitation was gone.

I believe i probably had the wrong power valve and I always felt as if the carb wasn’t giving the engine enough fuel at WOT so i jetted it up from 66 to 72 primary’s which was probably wrong to do.

I think the 10.5 PV will probably allow me to lean out my primary jet I have a primary jet of 72, and a secondary jet of 74 which is probably way to much for this teen.

Maybe I’ll try 70/72 jets
 
Slantsix64 said:
I actually do have a dash vacuum gauge for my 67 barracuda! @Mattax this is how I got my readings
Click to expand...
So glad mine came with that gage too.
1712840250455.png
:thumbsup:


Slantsix64 said:
If I have a 3k stall wouldn’t I want to have enrichment from the power valve sooner vs later @AJ/FormS ?

Thanks for everyone’s replies! I really do appreciate everyone’s input and personal opinions

I just installed the 10.5 power valve and wow, really responsive off the line at WOT, but I had a little hesitation at WOT so I tightened up my quick fuel adjustable secondary pot to have the secondaries come in later and the hesitation was gone.

I believe i probably had the wrong power valve and I always felt as if the carb wasn’t giving the engine enough fuel at WOT so i jetted it up from 66 to 72 primary’s which was probably wrong to do.

I think the 10.5 PV will probably allow me to lean out my primary jet I have a primary jet of 72, and a secondary jet of 74 which is probably way to much for this teen.

Maybe I’ll try 70/72 jets
Click to expand...

You can play with the secondary opening point, but its a bit of a guessing game. I'll come back to this.

The PV number has NOTHING to do with the fuel mixture. That's the opening point (vacuum) for enrichement.
At wide open throttle a 6.5 will be just as open as a 10.5 PV. In other words same fuel mix. The manifoild vacuum is 0 to maybe 3 inHg in a restrictive setup. The fuel mix at wide open throttle is adjusted by changing the power valve channel restriction (PVCR).
For many of us, thats not the way we do it at first. At first we change the primary jets.
IF the best jetting for high speed cruise and top gear wide open throttle is the same, then we're done.
IF the best jetting for high speed cruise and top gear wide open throttle are different, then the jetting for best (leanest) cruise is installed and the PVCR is changed to provide the AFR mixture that provides the best full power.
If the carb was setup correctly by the factory, part throttle mixtures will be fine and all we need to do then is find the vacuum where the PV should enrich the mixture.

Most of this ^^^^ is science and engineering. You can see examples on the datta logs I've posted, and the science is in engineering books like Larew's from which the AFR vs load diagram i(posted in the other thread) were developed.

As far as sequence and procedures, this is my opinion based on my experiences. Others will have different experiences so different opinions.

Playing with secondary opening point.
We can use this a bit to compensate for other things.
I've certainly done it.

The better way is to get primary side to do what it needs to do well. Then get the secondary side tuned to match. Its a bit of an iterative process.

We can isolate the secondaries from a test by delaying their opening or disconnecting them completely.
I find this can be useful. Others don't like to do this because it changes the airflow, especially at wide open throttle. But disconnecting will allow us to get the primary jetting pretty close and if AFR logging is available allow use to get the air bleeds correct for a flat consistant AFR delivery.

An advantage of working on a chassis dyno, with a cooperative operator, is expand the AFR scale to see if the AFR is staying flat.
In this example it was flat at first with the larger jets, but was drifting lean with the smaller jets. The high speed air bleeds are just a bit larger than they should be for those jets. If we only had those two pulls, we would not know if this was both primary and secondary circuits or just one of them.
Mattax said:
Here's how much was gained by changing jets.
70,74 to 66, 72
View attachment 1715473374
Click to expand...

This getting a bit off the initial focus on the power valve but where I'm going is the secondary opening should not be used for enrichment.
Secondary opening is for more air when the engine can use it. The fuel mix into that addtional air should be the same as the primary circuit's AFR at that same time.

In this post you can see an example of where the primary and secondary circuits are very different. Disconnecting the secondary side allowed me to tune the primaries for WOT. Then with the secondaries connected I knew all the changes had to be made to the secondary side.
 
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Newbomb Turk said:
A converter will affect power valve timing??

That’s dead wrong.
Click to expand...
Look, This is a daymn fine STREET 318.
This is NOT a race motor.
Op has a 3000 stall, on a high-pressure 318 with Magnum heads, in, I'm assuming, a 67 Barracuda. With this combo, the engine is very lightly/almost extremely lightly loaded, below that stall; and, I took the liberty of assuming, that he was not running hiway gears.
I mean; I'd probably be running 4.30s, for 60mph= ~5100rpm in Second gear.
But I'd think, OP is more likely to be in the 3.73>3.91 window.

I mean he already told us that it idles at 15/cruises at 22 inches, so it's got a lot of low-rpm torque; and,
I also assumed that he would be jetted too rich, cuz every 318 owner I ever knew, does it.
So then, what I said was;
"With a 3000 stall, the PV-calibration won't hardly matter."
I did NOT say that it does not matter at all.
I said, "won't hardly matter".
cuz;
OP's carb is rich enough on the Primaries, it might not even need a PV hardly at all. Please notice, I said "hardly at all"
Then; OP tells us that he's running 72P/74S, thus confirming my thoughts.
Notta chance does that 318 need a 72P. the 66P was probably real close, and the 72 is a good starting point for the Secondary, and now, the 10.5PV is gonna fill the gap, after the Primary runs out, just like it's supposed to.
I mean,
I suppose,
you mighta missed the part about
" won't hardly matter".

Tell me I'm wrong.
 
AJ/FormS said:
Look, This is a daymn fine STREET 318.
This is NOT a race motor.
Op has a 3000 stall, on a high-pressure 318 with Magnum heads, in, I'm assuming, a 67 Barracuda. With this combo, the engine is very lightly/almost extremely lightly loaded, below that stall; and, I took the liberty of assuming, that he was not running hiway gears.
I mean; I'd probably be running 4.30s, for 60mph= ~5100rpm in Second gear.
But I'd think, OP is more likely to be in the 3.73>3.91 window.

I mean he already told us that it idles at 15/cruises at 22 inches, so it's got a lot of low-rpm torque; and,
I also assumed that he would be jetted too rich, cuz every 318 owner I ever knew, does it.
So then, what I said was;
"With a 3000 stall, the PV-calibration won't hardly matter."
I did NOT say that it does not matter at all.
I said, "won't hardly matter".
cuz;
OP's carb is rich enough on the Primaries, it might not even need a PV hardly at all. Please notice, I said "hardly at all"
Then; OP tells us that he's running 72P/74S, thus confirming my thoughts.
Notta chance does that 318 need a 72P. the 66P was probably real close, and the 72 is a good starting point for the Secondary, and now, the 10.5PV is gonna fill the gap, after the Primary runs out, just like it's supposed to.
I mean,
I suppose,
you mighta missed the part about
" won't hardly matter".

Tell me I'm wrong.
Click to expand...

You are wrong. It matters, regardless of stall speed. The two are not related.
 
Stall rpm is arguably just a way to compare similarly manufactured torque converters.
Its common use I think obscures the operation and effect of converters on engine load.
I'm no expert on this. In general I think its safe to say that a lower stall rpm will have higher load on the engine at lower rpms. This means the engine will not tolerate less well tuned timing and AFR in the lower load, lower rpm ranges.

But the stall number itself may or may not tell us much. If we have a Turbo Action 10" called a 3000 rpm stall versus a 2600 stall, what does that mean?
Are those the nbumbers we'll see on a brake stall test? is it the rpm it will flash to when the vehicle is moving at WOT?
We know that the engine power and torque will effect even the brake stall when actually installed into a drivetrain.
We also know that when cruising at 60 mph at 2600 rpm, a 3000 rpm converter will not be slipping noticibly more than when driving 70 mph at 3000 rpm. Converter slip and stall vary with load. That said some designs have less power loss under light load, and all converters have some loss even at high rpm - hence their limited use for road racing and the advent of lock up converters for better mpg.

I'm not saying converter has no effect on the enrichment point. A looser converter might let us get away with a less well tuned carb and ignition and at times that might include the PV point. But its not a given or direct relation that I can see. I suspect that those who have set up lean idle mixes with lots of initial timing will see lean issues in the off-idle lower rpm range that might be 'fixed' with early enrichment. Of course this comes at a cost of possibly washing down the cylinders with excess fuel when not needed....
 
This discussion is a fine argument for EFI! Seriously, I switched to EFI just because of how difficult it is to get all of the analog circuits in a carb dialed in correctly in a dual purpose car. The power circuit (PV) is a great example of how a fairly simple valve can become super complicated in practice. As Matt points out, the power valve opens and closes the circuit, but the flow of fuel is controlled by the pressure drop (which changes depending on loading) and the size of the restriction. 90% of hot rodders don't even know what a PVCR is. Walk around a race track and ask racers if they have ever adjusted the size of their PVCR and you'll get a lot of blank looks. (Same with IFR and booster channel size)
Fortunately carb engineers have figured out most of this stuff over the years and if you buy a good carb like a Holley XP, they'll be very close right out of the box. We run carbs on race engines all the time on the dyno and good carbs work great right out of the box.
As for the OP, just try some different stuff and see what happens. It is a great way to learn. If you want an educated guess place to start then copy what the Holley engineers used in a carb designed for your application. An even better guess is to copy what the OEM engineers did back in the dark ages when they used Holley carbs. You have to go back in time about 50 years, but Holley carbs were used on everything from tow trucks to muscle cars so there are lots and lots of examples of how real engineers came up with compromises for power, fuel economy and reliability.
 
Update, So I jetted down the primaries from 72 to 66 Stock jet size and engine lost some vacuum and I had to raise the idle a hair. Now for sure there is a WOT hesitation only on WOT no where else, it’s a slight hesitation.

Why would I lose vacuum from a jet swap?

I’ll probably stick the 72s back in and wait until I get some 68 or 70s and try them out! Thanks guys!
 
Stop tuning WOT with the primary jetting. You’re going to tune yourself in to a corner. What was the cruise AFR with the 66 jets?
 
Stick a 68 jet and 6.5 power valve in, should be real close.
 
I’m thinking primary’s will be around 68-70 as well.

the carb out of the box had 66 primary and 67 secondaries metering plate and always felt it had a lean surge. (I swapped the plate to run conventional jets in the rear)

The 72/74 ran great no surge I don’t see any soot on my bumper or any smoke at WOT, so I believe I’m close

Thanks guys I’ll let you know how it all goes
 
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