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Benefits of removing Power Valve on Holley ?

Mike Gaines

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Ok...its winter time coming a I need to start a thread on something we all need to know and understand...
What benefit ( Best Wheels Up.jpgfor a drag race car only...nothing to do with a street/strip car) does removing the primary power valve on a Holley and then jetting up the primary side of the carb.
For example I have an 850 Demon with a 6.5 power valve with 83 primary and 90 secondary jets. All my pals are telling me to block off the power valve and jet to 88/88 square (or something like that)
I would appreciate the tons of knowledge you guys have to share it on this thread and educate all of us on the "power valve" deal.
Thanks..

PS: Working on the final tune on my new 505" .... mainly jetting and timing now, no traction problems...1.55 60' with front wheels up and NO breaking loose on the slick. My 1.55 60' is close to my target of 1.50 60' to end up with a 10.80 at 123-125 Qtr Mile time....but not jetted or timed right yet....Running 34 degrees with 50/50 mix of 91 pump and VP 110 for a net of 100 Octane.

Has run a 10.98 at 120.6 on the 5th run...
 
From what I understand of it...if you have low vacuum due to a large cam your power valve may not function properly.
 
The power valve is there to restrict fuel to the main jets and then open fully (no restriction) at the stamped vacuum level. I believe Holley recommends going up at least 4 jet sizes if you remove the power valve. I prefer to keep it in as it makes idling around easier on the plugs, etc.
Two reasons to remove it would be the low vacuum at idle previously mentioned and if the engine is prone to backfiring, you don't have to worry about it rupturing.
 
taking the power valve out of a holley is basically giving the carb a lobotomy. it's full time main metering. as said in the previous post that if manifold vacuum is too low to activate the power valve then it will need to be removed. the proper way to jet up after removal of the power valve is to measure the area of the power valve channel restriction, add this the the jet area being run, and then pick a jet that has the same jet area as the both combined. but, i've learned a long time ago not to argue or get technical with a bracket racer. just let your "pals" get their hatchets out.
 
I'm running a hemi with crossram and factory holleys w/power valves, I had a conversation with Ray Barton this year about his intake and he asked what I was running and he said to try it with out the power valves and jet up 6 numbers, he said it makes the car react quicker off the starting line, cause you don't have to wait for the carb circuits to work, I still haven't tried it yet , maybe next year, he did say it'd be a little dirtier (richer) driving around the pits etc.
Russ
 
I agree with what lew said. That said, however, part of the fun of having a race car is trying different tweaks and charting what helps or hurts YOUR combination.
As has been said, the first thing to do is to check the vacuum reading with the engine at operating temperature. The power valve you use should reflect 1/2 the amount of vacuum at idle; that is, if you have 13" of vacuum, use a 6.5 P/V. In my own experience, my race motors all had too little vacuum to properly hold a P/V closed, so I blocked them off and up-jetted an equivalent size, pretty much as lew explained. All the other points concerning idle quality and plugs are valid.
 
Every thing I have read above this post of mine sure makes a lot of sense about power valves. Keep the cards and letters coming...more info and thoughts the better.
Thanks....
 
keep the power valve , the engine will last longer not running dirty in the lower rpm, a rich fuel mixture will wash oil of the cyl wall , dilute the oil with raw fuel, load up the spark plugs sooty & carbon fouled , also a power valve that is higher rating than what the engine vacuum pulls at idle WILL NOT make the idle rich, the throttle blades are in the idle,transition slots,the main s are not flowing fuel at idle if the carb is set up properly.
 
i am with CDR , I have 4.5-5.0" vacuum in gear and I run a 6.5 quickfuel power valve.no problems in my daily driver/strip car .
if worried about opening think of this . you are footbraking to mid 2000rpm - you have load and rpm the PV is more than likely open ,unless you have a very low PV number , plus you will be pulling on the main jets as well .

Tex
 
taking the power valve out of a holley is basically giving the carb a lobotomy. it's full time main metering. as said in the previous post that if manifold vacuum is too low to activate the power valve then it will need to be removed. the proper way to jet up after removal of the power valve is to measure the area of the power valve channel restriction, add this the the jet area being run, and then pick a jet that has the same jet area as the both combined. but, i've learned a long time ago not to argue or get technical with a bracket racer. just let your "pals" get their hatchets out.

lew, your suggestion for jetting is right on. This coming from a bracket racer who does understand some of the technical stuff. A race car with a big cam has no need for a power valve. Also the power valve adds one more variable in the carb equation. That's a concern for for bracket racers.
 
lew, your suggestion for jetting is right on. This coming from a bracket racer who does understand some of the technical stuff. A race car with a big cam has no need for a power valve. Also the power valve adds one more variable in the carb equation. That's a concern for for bracket racers.

I agree. I pulled the PV out of my bracket car and never looked back. Way better. More consistent. Don't have to worry about one other thing failing at the most inopportune time. On a car that sees street driving too.... leave it in.
 
I agree. I pulled the PV out of my bracket car and never looked back. Way better. More consistent. Don't have to worry about one other thing failing at the most inopportune time. On a car that sees street driving too.... leave it in.

Thanks for reminding me I left out the fact that on a street driven unit the power valve does serve a very important role. My current car is "street/strip" and I have a 4.5 power valve. However for strip use there is no need for it.
 
IMO power valves are used on street cars only. Block it off and square the jets. From the info u gave, 88 jets are a good (safe) starting point, but if I had to guess it will want more. The proven method( for us simple bracket racers) for finding the best jet size to run, is to keep going up in jet size until you lose mph. Once car loses mph, jet back to the previous run and you should be real close to the optimum fuel ratio for your combination. Or put in O2 sensors and get a AF meter. Either way you don't need or want a PV on a full out drag car engine.
 
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I run a power valve on my 63 since its a street car and pulls enough vacum to work it. If my car was race only then I would not run them. Ron
 
IMO power valves are use on street cars only. Block it off and square the jets. From the info u gave, 88 jets are a good (safe) starting point, but if I had to guess it will want more. The proven method( for us simple bracket racers) for finding the best jet size to run, is to keep going up in jet size until you lose mph. Once car loses mph, jet back to the previous run and you should be real close to the optimum fuel ratio for your combination. Or put in O2 sensors and get a AF meter. Either way you don't need or want a PV on a full out drag car engine.
dead on there Al.as said before,power valve is for street use.for full race,take it out.no need to complicate things when you are looking for consistant times.test and tune is your friend!
 
I've run Holley's on my car and Edelbrock's. The Holley's had the power valves blocked. Holley's started way easier cold, but sound ratty and are mushy driving around the pits. The Edelbrocks still have metering rods with the stock springs. The equivelent of having power valves. They have more throttle response and drive great around the pits. Either set is with-in about .05 on my 9.0 car. Cam is [email protected]". My bet is power valves can be made to function. However the only thing quicker about the Holley's is the 60 ft. Could it be the lack of power valves? Maybe I'll try fixing the rods in the stationary open posistion in the Edelbrock's and see if it helps. I can definitely say they would drive better around the pits with power valves installed. As far as keeping the plugs clean, the car hasn't had a set of plugs in 275 passes so I guess that's not an issue. Also a note; I never clean it out or free rev it.
Doug
 
taking the power valve out of a holley is basically giving the carb a lobotomy. it's full time main metering. as said in the previous post that if manifold vacuum is too low to activate the power valve then it will need to be removed. the proper way to jet up after removal of the power valve is to measure the area of the power valve channel restriction, add this the the jet area being run, and then pick a jet that has the same jet area as the both combined. but, i've learned a long time ago not to argue or get technical with a bracket racer. just let your "pals" get their hatchets out.

There is no too low, unless the PV # rating is too high or greater than manifold vacuum=could open at cruise somehow. The vacuum is what holds it closed.
 
keep the power valve , the engine will last longer not running dirty in the lower rpm, a rich fuel mixture will wash oil of the cyl wall , dilute the oil with raw fuel, load up the spark plugs sooty & carbon fouled , also a power valve that is higher rating than what the engine vacuum pulls at idle WILL NOT make the idle rich, the throttle blades are in the idle,transition slots,the main s are not flowing fuel at idle if the carb is set up properly.

I respectfully disagree. If you've ever had an older Holley that suffered a backfire and ruptured the P/V diaphragm, you've seen just how rich it can make the engine idle. The P/V channels do not go through the main circuit. Washing down the cylinder walls due to the up-jetting required when you remove P/Vs is not a concern in a RACE ONLY motor. Up-jetting correctly does not DUMP fuel into the cylinders like a stuck needle & seat or too much fuel pressure.
As has been said, a RACE ONLY bracket car doesn't need more variables, and works just fine without the P/Vs.
 
I respectfully disagree. If you've ever had an older Holley that suffered a backfire and ruptured the P/V diaphragm, you've seen just how rich it can make the engine idle. The P/V channels do not go through the main circuit. Washing down the cylinder walls due to the up-jetting required when you remove P/Vs is not a concern in a RACE ONLY motor. Up-jetting correctly does not DUMP fuel into the cylinders like a stuck needle & seat or too much fuel pressure.
As has been said, a RACE ONLY bracket car doesn't need more variables, and works just fine without the P/Vs.


If the power valve has a blown diaphram it will make the idle very rich as it will pull fuel right through the valve to the manifold vacum on the other side of the valve diaphram and run rich. If the power valve is just open at idle when its not enough vacum to hold it closed then it wont run richer since the main circuit that feeds the venturi is not working yet when its idling and running on just the idle circuit. Only if the valve diaphram is blown will it run rich sucking fuel right through the diaphram from manifold vacum on the other side of the diaphram. Ron
 
I respectfully disagree. If you've ever had an older Holley that suffered a backfire and ruptured the P/V diaphragm, you've seen just how rich it can make the engine idle. The P/V channels do not go through the main circuit. Washing down the cylinder walls due to the up-jetting required when you remove P/Vs is not a concern in a RACE ONLY motor. Up-jetting correctly does not DUMP fuel into the cylinders like a stuck needle & seat or too much fuel pressure.
As has been said, a RACE ONLY bracket car doesn't need more variables, and works just fine without the P/Vs.

a blown power valve has about as much to do with the ORIGINAL question as a stuck open needle & seat.

you can do it your way & i will do it mine .
 
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