Holley Power Valve Experimentation

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12many said:
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.
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I was referring to this post below.
RustyRatRod said:
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.
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Oldmanmopar said:
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

Also the face of the brass plunger is the seal of the PV on the body of the carb The vacuum source pulls on the opposite side of the spring not the threaded side. So if you change the length of the plunger you are defeating the seal. Make it to short it will be open all the time.
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I'm not sure I'm following what your describing. Do you have a picture?
 
92b said:
I'm not sure I'm following what your describing. Do you have a picture?
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ring-block-screw-in-power-valve-restrictors-scaled.jpg
 
Down a rabbit hole, into the abyss.
Propane torch carefully applied on the disc to loosen the loctite, and it’s easily unscrewed (Diaphragm in no way gets damaged) Definitely can then screw the disc down for more preload on the existing spring. But will this alter its closing/opening without a stiffer spring. I really doubt it. Finding a spring with slightly thicker wire diameter in the .027”.-.029” range and close to OD, height and rate proving fruitless. But then there is this option:



Now we just need a lathe and some other equipment LOL. I’d just use a drill and a rod with a hole in it and improvise. Found some cheap music wire in the size needed, ideal for making a spring, enough to experiment with. Maybe:rolleyes:

8646B4F0-C293-4ADA-958B-9FBB83182D6D.jpeg
 
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12many said:
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?
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Yeah…get a power valve tester and you’ll be shocked. I check every PV because they aren’t exactly exact.
 
Oldmanmopar said:
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
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Come on man. That is JUST WRONG.

This myth needs to die a quick death.

This is just one reason why holleyitis exists.
 
OK, we might be getting somewhere. @RustyRatRod was correct on shimming, using a washer or as it turn out screwing down the disc. The threads are 10-32. After cleaning the loctite off, the disc threads on easily. Did a quick test on a disassembled 4.5” Hg PV. Disc at original height, flush with stud, then screwed it all the way down, then back to flush. Used a thin wire that would show deflection. Crude yes, but clearly shows it takes more force to close the valve after the preload is added. The disc screwed all the way down does bunch up the spring and restricts or blocks the valve somewhat, but with some testing might only need to be screwed down 1/2 way or at a point where still unrestricted or closed up too much.What do you think??



Tester on the way to more precisely measure, hopefully.
 
You might be on to something indeed! Nice work!
 
Oldmanmopar said:
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

Also the face of the brass plunger is the seal of the PV on the body of the carb The vacuum source pulls on the opposite side of the spring not the threaded side. So if you change the length of the plunger you are defeating the seal. Make it to short it will be open all the time.
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I should have said it was the second paragraph I didn't understand. Thanks for the video.
 
I tuned my Q series QFT 750dp with a 9.5 4 window by simply stretching the existing spring. It opens around 12". I run a 69 PJ with .070 PVCR to keep the highway cruise at 14.5 and WOT at 12.5 with a 86 SJ. With a 9.5 PV the car had a slight stumble rolling the throttle with primaries only. I chose to not cover the stumble with more pump shot. The spring stretch cured the stumble (added fuel when I needed it). At the track my AFR is still good when stomping the pedal during launch. If you understand how all the different circuits of a carb work you soon realize that there is more than one way to get it done. I use my car as street/strip and this works for me.
 
mderoy340 said:
I tuned my Q series QFT 750dp with a 9.5 4 window by simply stretching the existing spring. It opens around 12". I run a 69 PJ with .070 PVCR to keep the highway cruise at 14.5 and WOT at 12.5 with a 86 SJ. With a 9.5 PV the car had a slight stumble rolling the throttle with primaries only. I chose to not cover the stumble with more pump shot. The spring stretch cured the stumble (added fuel when I needed it). At the track my AFR is still good when stomping the pedal during launch. If you understand how all the different circuits of a carb work you soon realize that there is more than one way to get it done. I use my car as street/strip and this works for me.
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I kinda figured theres gotta be people out there that want to run something more than a 10.5 and found a way to make it work. Impossible to find anything posted about what they’ve done that’s for sure. Did you just stretch and drive it watching the gauge and adjust or bench test the valve to get it close first then adjust?
Thanks for posting what you’ve done. I’ve searched and searched the web and your post is (seriously) the first I’ve read of a method with results.
Ive got a tester on the way and will adjust the disc to preload the spring, hopefully see what it yields.
:thumbsup:
 
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12many said:
I kinda figured theres gotta be people out there that want to run something more than a 10.5 and found a way to make it work. Impossible to find anything posted about what they’ve done that’s for sure. More than one way to skin a cat here. Did you just stretch and drive it watching the gauge and adjust or bench test the valve to get it close first then adjust?
Thanks for posting what you’ve done. I’ve searched and searched the web and your post is (seriously) the first I’ve read of a method with results.
Ive got a tester on the way and will adjust the disc to preload the spring, hopefully see what it yields.
:thumbsup:
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I dialed my car to run 12.5 AFR with a dual plane air gap with all plugs burning even and worked backwards to dial in an optimized cruise to drive 50 miles make minor changes and race. I favor my car to run better at the track than cruise. I ran a vacuum gauge to manifold and ported vacuum to see what was going on. The stumble occurred accelerating in 3rd gear on the on ramp to the interstate if I drove like a normal person. If I went up one PJ number the stumble went away but my cruise AFR got to fat. I'm stock stroke 340 with 4.56 gear and gear vendor OD cruise at 3K rpm. I'm sure a stroker would be a different setup due to booster velocity. Everyone needs a different setup with all the variables involved; cid, car weight, carb cfm, rear gear, etc. I run demon metering blocks for a flat fuel curve at the track, 3 hole .025/.025/.026, IFR .032 bottom of block. I did test after spring stretch using an old metering block and the large suction cup with a short hose on my hand pump. I cruise at 15" and needed to have 12" ballpark opening. The 12" worked for me and it also helped passing throttle. Car is very snappy running on just the primaries.
Here's my carb setup and I run at sea level.
PJ 68H 69H
SJ both 86H
IFR .032 bottom block 4 corner idle at 7/8 turn
PVCR .070
Blue cams #1 hole 37/39 nozzles
metering block 3 hole .025/.025/.026
Idle AB .067 all 4 street driving. I change the primaries to .063 at the track to fatten the idle up with my headers uncapped.
Timing is 28* intial 34* total mechanical, vacuum advance on ported and cruise at 48* total.
Many folks make the mistake of changing primary jets when they are actually still running off the idle circuit. Also an open power valve does not flow fuel until fuel flows thru the booster. Engine vacuum at idle will pull fuel thru a blown power valve.
Happy Tuning.
 
Cool the mechanical complexity of a Holley, but still nothing compared with the Bosch Jetronic mechanical fuel injection on 1990's Euro cars (incl. Delorean). Those are like a fine Swiss watch with jewel movements and even a mechanical fuel distributor. If you want simple, go Carter -> Edelbrock, though fooling with metering rods can be tricky.

I put a Holley Commander 950 TBI on my 1965 383, but couldn't get it to idle reliably. At least you can make all adjustments on a PC. Problem is old software and finicky (Win XP max) and Holley no longer supports it. Many problems were software glitches, like it would start not firing, I'd login to the controller and find the whole fuel map botched with strange numbers. Finally found aftermarket auto-tune software for $15, which helps a lot. Need to switch to a wideband O2 sensor to make tuning easier and more precise. That is a wise thing for tuning a carburetor too, so you aren't flying blind.
 
What I did was take the PV right out, and installed a plug . then put my vacuum gauge on the windshield , plumbed to the intake. Then road tested it to see what the engine wanted. Pretty quick I figured out that she wanted something around 10/11
Then the testing began, but first I had to learn how to use that tool, cuz it was spitting out numbers that had nothing to do with the codes on the valves.
Since I was pretty sure my gauge was accurate; I calibrated all my valves according to it. then I just selected what I thought was about right, and screwed it in, and bingo. Beautiful, smooth roll-ons.
My valves were a mix of new and used, and it seemed like the used ones were closer to correct than were the new ones.
 
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