rear power valve on HP holley should i run one ?

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speedy

rear power valve on HP holley should i run one ?

Post by speedy »

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.
Ed-vancedEngines

Post by Ed-vancedEngines »

how many inches of idle vacuum do you have in gear if automatic? If clutch, same question, but how many inches of vacuum in neutral at idle rpm?

I use power valves and I like the power valves on everything that has enough vacuum and is not subject to tremendous manifold pressures.

If you eliminate a proper sized power valve, I suggest to step the jets up by 3 to 4 sizes to start with.

Ed
Last edited by Ed-vancedEngines on Sat Feb 03, 2007 2:17 am, edited 1 time in total.
speedy

Post by speedy »

on my last combo i had 13 in hg at idle but im upping the combo i guess it will be around 10-11in hg, im thinking the fuel will slosh away from the power valve in the rear bowl. i will be running a pv in the front, its the rear one that worries me. thanks ed.
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Post by fishman »

If this car is just use on the track remove the rear power valve and go up 6 to 8 jet sizes if this car is being used on the street u want to keep the power valve or the car will run rich at idle.......your choice but i use a power valve on my street rod and my race car i don't because of a vacuum issue on the race car but not on the street car...so i guess maybe i should ask if it is a street car with huge lift then yes remove the power valve
speedy

Post by speedy »

it is a street/strip car, i dont understand how it could make it rich at idle seeing as the secondary circut isnt operating at idle.?
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Post by maxracesoftware »

speedy wrote:it is a street/strip car, i dont understand how it could make it rich at idle seeing as the secondary circut isnt operating at idle.?
4-corner idle Carb ? what CFM Carb ..what LIST Number
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I dont run a rear PV after a rebuild

Post by My427stang »

Generally, not always but almost always, I pull it out the rear and jet up 8 numbers to make sure I am not lean at WOT. In other words, if its got 72's I go 80's in the rear.

Its another moving part that IMO doesnt help much in most situations

If you were running WOT road racing, coming in and out of the secondaries, I would think it would add some tuning capability by allowing it to be a little richer at tip-in of the secondaries then lean out as load decreased

However, not a whole lot of people run that way, and a WOT jab going through the gears, the main well will have fuel either way, and the PV only adds more possibilty to become uncovered like you said, and a top end lean condition if it closes

I always run a front PV, otherwise the circuit is just too rich, but the rear I think plugging is smart

Watch the plug during assembly though, sometimes you have to grind the top off a bit so it doesnt hit the body of the carb when you install the metering block. It'll drive you crazy because it'll keep the metering block from sealing but they are usually close enough that it wont break anything. 10 seconds on a bench grinder is adequate to peel off the raised edge

Also, the main circuits dont affect idle, PV or not. Fuel through the idle and transition circuits are seperate from the booster circuits that the PV and main jets feed.

If they did, you either have a porosity problem, fuel traveling across the metering surface, or your throttle position is too far open and you have airflow across the booster

The secondary idle circuit does operate at idle on all Holleys though, theory here is more to prevent stale fuel in the rear bowls in grandpa's car, but in modern Holleys, it also allows better idle distribution, regardless, it's a different circuit and in proper operation shouldnt be affected by PV or no PV

I run a 1000 HP series on my own car and did the same thing
rmcomprandy

Post by rmcomprandy »

NO power valves ... drag race mentality !!!

If it is working correctly a power valve will NEVER hurt.
OVAL track mentality !!!

On the secondayy side ... if you are ever doing any kind of hard braking or competitive deceleration, then you need it.
Road Race mentality !!!
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power valves

Post by bigjoe1 »

On drag race only carbs, it is best to plug the rear and use jet extentions This will help from uncovering the rear jets and power valves on the starting line .Depending on the carb, 5 to 8 jets sizes must be increased since no fuel will go thru the power valve now.JOE SHERMAN RACING
speedy

Post by speedy »

my427stang, my thoughts exactly, i cannot see how a rear power valve can affect idle quality, the power valve circut will not work at idle unless its faulty or rated way to low. ive noticed a couple of guys are saying you must run a front pv, that wasnt the question, i asked about the rear one only. yes i will be running a front pv. i agree with you bigjoe1 i think the rear power valve will be uncovered on hard accelleration, which wouldnt show up on a dyno with the car stationary.
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Re: rear power valve on HP holley should i run one ?

Post by MadBill »

I know this thread is ancient, but if anyone is reading it they might like to know that power valve caps are (or at least have been in the past) available to mitigate slosh. They are a snap-fit over the valve and draw their fuel from a hole at the bottom.
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Re: rear power valve on HP holley should i run one ?

Post by steve cowan »

MadBill wrote: Sat May 02, 2020 12:42 am I know this thread is ancient, but if anyone is reading it they might like to know that power valve caps are (or at least have been in the past) available to mitigate slosh. They are a snap-fit over the valve and draw their fuel from a hole at the bottom.
Hi Bill,
Can't find those caps in Australia but I can purchase a set of Braswell 2 circuit metering blocks with cast in covers over the powervalve area, have you used the bottom feed needle and seats to help control fuel froth??
I have 3 x holleys and 1 x demon carb that I always use rear powervalves and 1:1 throttle butterfly with square jetting seems to work for me on my stuff.
Was reading some of your old posts, like the idea of building a test rig for exhaust port testing with heated compressed air and some of Clints pressure sensors. :D
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Re: rear power valve on HP holley should i run one ?

Post by bill jones »

--this is what I have been making for years---using a lathe and a mill

---.450" OAL x .620" OD aluminum bar stock with a .540" ID recessed hole .420" deep
---machine the power valve fuel hole .620" x .220" deep using a 2 flute end mill that has been stoned slightly smaller to get the good press fit

---inside recess needs to barely clear the brass end of the relaxed power valve
---the center of the brass end needs to be ground away if it protruded out past thru center of the brass end
---overall length sticking out needs to clear the float

---hole for the fuel entry needs to be done after it's pressed in--so that hole doesn't cause the aluminum thimble to crumple when pressing it in

--green Loctite might save the day if the press fit is too loose
POWER VALVE CAPS ETC.jpg
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Re: rear power valve on HP holley should i run one ?

Post by MadBill »

steve cowan wrote: Sun May 03, 2020 3:37 pm
MadBill wrote: Sat May 02, 2020 12:42 am I know this thread is ancient, but if anyone is reading it they might like to know that power valve caps are (or at least have been in the past) available to mitigate slosh. They are a snap-fit over the valve and draw their fuel from a hole at the bottom.
Hi Bill,
Can't find those caps in Australia but I can purchase a set of Braswell 2 circuit metering blocks with cast in covers over the powervalve area, have you used the bottom feed needle and seats to help control fuel froth??
I have 3 x holleys and 1 x demon carb that I always use rear powervalves and 1:1 throttle butterfly with square jetting seems to work for me on my stuff.
Was reading some of your old posts, like the idea of building a test rig for exhaust port testing with heated compressed air and some of Clints pressure sensors. :D
I haven't tried bottom feed N/Ss Steve, but they look like a great idea after viewing videos of what can be happening in there. #-o

I had no trouble sourcing PV caps in the seventies and a few years ago I could still find one source, but I don't remember the name. Curious that they've fallen out of favor; it's not like launch gs are decreasing. They looked exactly like Bill's work, except in brass. Under ten bucks, AIR... Unfortunately I don't think Bill could price-match that... :lol:

With a little luck, one might find a bottle cap the right size:

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Re: rear power valve on HP holley should i run one ?

Post by ClassAct »

MadBill wrote: Sat May 02, 2020 12:42 am I know this thread is ancient, but if anyone is reading it they might like to know that power valve caps are (or at least have been in the past) available to mitigate slosh. They are a snap-fit over the valve and draw their fuel from a hole at the bottom.


Who makes those caps?? I’ve heard of these things, yet never seen one, nor found anyone who can tell me where I can buy them.

TIA
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