Holley Power Valve Experimentation

[12many]

Tinkering out in the shop with some power valves after @RustyRatRod mentioned in another thread about using an e-clip to retain the disc to reassemble after a spring change, one possible method of disassembly/reassembly in order to use a heavier spring to create an 11.5-up power valve(s)
Removing the spring is obviously the easy part without cutting mods or damage. Sourcing a spring to create the correct value (in. Hg) not so much. I measured all the pv’s springs I have on hand as best I could (* in picture denotes PV I don’t have, the wire diameter shown is assumed) Seems each step up in rating has .001” thicker diameter wire and the overall width goes up and the height down slightly. Very hard to get an accurate height reading. A straight edge does lay pretty much flat across them.
Time to start looking for springs that could be cut down and ends formed to seat correctly. Would take some testing to ensure they open at the correct vacuum. Sure wokld be nice to have higher than 10.5 pv’s to try out. May be a bust but worth a try.

 

[Bewy]

I do not mess with Holley junk, but I imagine the PV rubber diaphragm offers some resistance & would need to be factored into the reqd spring tension.

 

[RustyRatRod]

Tinkering out in the shop with some power valves after @RustyRatRod mentioned in another thread about using an e-clip to retain the disc to reassemble after a spring change, one possible method of disassembly/reassembly in order to use a heavier spring to create an 11.5-up power valve(s)
Removing the spring is actually the easy part (as shown) without cutting mods or damage. Sourcing a spring to create the correct value (in. Hg) not so much. I measured all the pv’s springs I have on hand as best I could (* in picture denotes PV I don’t have, the wire diameter shown is assumed) Seems each step up in rating has .001” thicker diameter wire and the overall width goes up and the height down slightly. Very hard to get an accurate height reading. A straight edge does lay pretty much flat across them.
Time to start looking for springs that could be cut down and ends formed to seat correctly. Would take some testing to ensure they open at the correct vacuum. Sure wokld be nice to have higher than 10.5 pv’s to try out. May be a bust but worth a try.



View attachment 1716026247

View attachment 1716026248

Ok so the spring rate goes up as the vacuum opening increases. I wonder if stretching the spring just a little would do it? Crude, I know. You can get a power valve tester to see.

 

[RustyRatRod]

Tinkering out in the shop with some power valves after @RustyRatRod mentioned in another thread about using an e-clip to retain the disc to reassemble after a spring change, one possible method of disassembly/reassembly in order to use a heavier spring to create an 11.5-up power valve(s)
Removing the spring is actually the easy part (as shown) without cutting mods or damage. Sourcing a spring to create the correct value (in. Hg) not so much. I measured all the pv’s springs I have on hand as best I could (* in picture denotes PV I don’t have, the wire diameter shown is assumed) Seems each step up in rating has .001” thicker diameter wire and the overall width goes up and the height down slightly. Very hard to get an accurate height reading. A straight edge does lay pretty much flat across them.
Time to start looking for springs that could be cut down and ends formed to seat correctly. Would take some testing to ensure they open at the correct vacuum. Sure wokld be nice to have higher than 10.5 pv’s to try out. May be a bust but worth a try.



View attachment 1716026247

View attachment 1716026248

How are the discs on the threaded ends secured? Are they staked? Self locking threads? I wonder about removing the discs and putting some washer(s) between the spring and disc? OR maybe if you could just tighten the disc down and tighten the spring up? Results easily checked with a power valve tester.

 

[RustyRatRod]

I do not mess with Holley junk, but I imagine the PV rubber diaphragm offers some resistance & would need to be factored into the reqd spring tension.

I just BET that Holley style carburetors have won more races than any other type of carburetors combined.

 

[12many]

Ok so the spring rate goes up as the vacuum opening increases. I wonder if stretching the spring just a little would do it? Crude, I know. You can get a power valve tester to see.

I’m looking at the Moroso tester, trying to sift through the reviews to see if putting a specific vacuum on it will be accurate other than merely as a leak tester. Anyone have experience with one or from another brand or options for accurate measuring?

 

[RustyRatRod]

I’m looking at the Moroso tester, trying to sift through the reviews to see if putting a specific vacuum on it will be accurate other than merely as a leak tester.

Can a leak tester apply vacuum? I have one and I don't even know. lol

 

[12many]

Can a leak tester apply vacuum? I have one and I don't even know. lol

Just discovering it all. Using a specific vacuum on the tool with a valve in it should tell the tale I’d think. Maybe someone here has more knowledge about it and if you can get accurate results at various vacuum numbers? By the looks of it I assume you decrease the vacuum below the PV value and it should open?

 

[RustyRatRod]

Just discovering it all. Using a specific vacuum on the tool with a valve in it should tell the tale I’d think. Maybe someone here has more knowledge about it and if you can get accurate results at various vacuum numbers

View attachment 1716026263

I was just reading the instructions on it. Hell I might get one. I need a new vacuum pump anyway. LOL Have to wait till payday though. It'll be worth it for good tuning tools, though.

 

[Oldmanmopar]

I ran a 2.5 PV to start We used a digital vacuum pump and a moroso tester. As soon as it moves record the vacuum , That is what you would read. Vacuum at idle divided by two or less is the size PV you want to start with. After its installed you can fine tune the number using your EGT gauge . Better to start lean then rich. Most street holley's come with a 6.5 PV commonly used for 13-15 in hg

 

[12many]

We used a digital vacuum pump and a moroso tester. As soon as it moves record the vacuum , That is what you would read.

That’s what I was thinking. Something to apply a measured vacuum other than a mighty vac or hand pumped type would be ideal.

 

[Demonic]

I’m certain China Freight has cheap vacuum pumps. A bit of pipe, a large face vacuum gauge or a compound gauge and a bleed valve on the other end of the tee gets you there. Just need to determine the thread on a Holley PV and you got it.

Vac pump has lots of uses in the garage anyway.

 

[12many]

I wonder about removing the discs and putting some washer(s) between the spring and disc?

If adding washer(s) I’d use a soft copper washer and make a straight cut, give it a tweak to work it over the stud, and bend it back to flat and put the spring on. I’m pretty sure shimming the spring would only add preload.

 

[70 Buster 340]

What is the application that would need a greater than 10.5 PV ?

 

[RustyRatRod]

If adding washer(s) I’d use a soft copper washer and make a straight cut, give it a tweak to work it over the stud, and bend it back to flat and put the spring on. I’m pretty sure shimming the spring would only add preload.

More preload is what we're after, right? A stronger or more compressed spring will make the valve open at a higher vacuum reading.......right? This isn't a rate thing, it's a when thing. Opening from say 9.5 to 12.5 just needs a stronger or more compressed spring, correct? Might can get by with just tightening the disc a few turns. As long as the valve opens at the vacuum reading you're looking for, you've achieved the objective, right? I just don't think it's that complicated.

 

[RustyRatRod]

What is the application that would need a greater than 10.5 PV ?

Could be anything. It's not the application, but how you tune. If you tune for a power valve at cruise vacuum reading, you can easily need a power valve beyond 10.5. What Holley has preached for years about power valve selection is WRONG and they've just now started admitting that. Their formula for idle vacuum divided by 2 is safe for them and easy for those who don't do a lot of precise tuning.

 

[12many]

More preload is what we're after, right? A stronger or more compressed spring will make the valve open at a higher vacuum reading.......right? This isn't a rate thing, it's a when thing. Opening from say 9.5 to 12.5 just needs a stronger or more compressed spring, correct? Might can get by with just tightening the disc a few turns. As long as the valve opens at the vacuum reading you're looking for, you've achieved the objective, right? I just don't think it's that complicated.

Maybe so. My experience with springs is with motorcycle suspension. Anything else I need to study more!

 

[12many]

What is the application that would need a greater than 10.5 PV ?

Definitely a vehicle that sees street action. If you drove two identical vehicles: one with a “Holley method” of 1/2 of idle vacuum and the other one done by 1/2 of cruise vacuum you would see immediately which is the correct method. Most obvious realization would be at various part throttle (primaries only) operation. But you can’t just slap in a higher number PV and roll. You have to tune all the circuits, one at a time in correct sequence. Seeing/feeling is believing.

 

[RustyRatRod]

Definitely a vehicle that sees street action. If you drove two identical vehicles: one with a “Holley method” of 1/2 of idle vacuum and the other one done by 1/2 of cruise vacuum you would see immediately which is the correct method. Most obvious realization would be at various part throttle (primaries only) operation. But you can’t just slap in a higher number PV and roll. You have to tune all the circuits, one at a time in correct sequence. Seeing/feeling is believing.

I go a bit more than half cruise vacuum. Mine for instance is 14hg at cruise. So I want about 2 under that. But the 10.5 is all that's available. It does make a big difference too. You're right on the money about that.

 

[12many]

I go a bit more than half cruise vacuum. Mine for instance is 14hg at cruise. So I want about 2 under that. But the 10.5 is all that's available. It does make a big difference too. You're right on the money about that.

In my stroker van on the street at light steady cruise even at highway speeds I can often see, believe it or not, 21hg, but on average about 18-19hg or so. As indicated by a SW panel mounted gauge. My idle vacuum is about 8-9hg in gear and about 11-12hg in park. This all matches a handheld vac gauge I have used before the gauge. If I used half of in park idle that’d be about a 6.5 but in gear a 5.5
The thing would never open until I really got into the throttle. There’d be nothing at all on the primaries under any amount of load until I got into the secondaries heavily. Nothing like feeling the power kick in even more from the PV with various light throttle only on the primaries.
Just like someone experiencing a tight higher stall converter for the first time it changes what you may have believed prior

 

[RustyRatRod]

In my stroker van on the street at light steady cruise even at highway speeds I can often see, believe it or not, 21hg, but on average about 18-19hg or so. As indicated by a SW panel mounted gauge. My idle vacuum is about 8-9hg in gear and about 11-12hg in park. This all matches a handheld vac gauge I have used before the gauge. If I used half of in park idle that’d be about a 6.5 but in gear a 5.5
The thing would never open until I really got into the throttle. There’d be nothing at all on the primaries under any amount of load until I got into the secondaries heavily. Nothing like feeling the power kick in even more from the PV with various light throttle only on the primaries.
Just like someone experiencing a tight higher stall converter for the first time it changes what you may have believed prior

Mine (slant 6) has a whopping 6hg at idle (manual transmission) and 14 at cruise. I went from the 6.5, to 3.5 and finally to 10.5 and by far, the 10.5 runs best. I think it would be pretty cool to figure out how to manipulate the opening.

 

[70 Buster 340]

Could be anything. It's not the application, but how you tune. If you tune for a power valve at cruise vacuum reading, you can easily need a power valve beyond 10.5. What Holley has preached for years about power valve selection is WRONG and they've just now started admitting that. Their formula for idle vacuum divided by 2 is safe for them and easy for those who don't do a lot of precise tuning.

So it is ... the application for a greater than 10.5 would be a street driver with high cruise vacuum.

What makes the Holley formula 'safe' for them?

 

[RustyRatRod]

So it is ... the application for a greater than 10.5 would be a street driver with high cruise vacuum.

What makes the Holley formula 'safe' for them?

Just using cruise vacuum period. Mine is only 14 at cruise and I sure wouldn't call that "high". It's simply a different way to tune.

The Holley formula is easier for the end user. Requires much less interaction and that equals less returns and warranty issues with Holley. = Safe for them.

 

[Oldmanmopar]

You all have to remember to divide your vacuum in half and go 1 or 2 numbers less so 15 would take a 6.5 PV to start out with. Common factory engine Vacuum 15 and usual PV that comes in Street carbs is 6.5 as stated. Quick fuel or Proform's usually have a 4.5 to start

 

[12many]

Might be referring to some other design of power valve. If one actually has one in hand, looks at these power valves with the spring on or removed like I’ve shown in the video, you see the plunger, or valve, all extend open and seat the same. No different than the height of a spring retainer installed on a valve and the spring pocket on a head. You remove the spring and replace it with a slightly stiffer spring of same od and height. Open/closed overall travel has not changed. Hope that clears it up for some. So, there is no changing it’s range of travel from open/closed. All that’s being done or proposed is an incremental spring rate change. Finding a spring that’ll work is the possible fly in the ointment here.