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B.A.M aka "Black Azz Mike
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I am going to dump the pv on my 800 holley. The motor is a 454 mag ho with a weiand 177 blower. I have heard that you pull the pv and you must go up in jets. If I do so, how many jet sizes do I go up? Do you have to run the PV on a blower motor? Any info is greatly appreciated :)

Spitter
 

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Cantard
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I am going to dump the pv on my 800 holley. The motor is a 454 mag ho with a weiand 177 blower. I have heard that you pull the pv and you must go up in jets. If I do so, how many jet sizes do I go up? Do you have to run the PV on a blower motor? Any info is greatly appreciated :)

Spitter
All I know is that a pv is worth 8-10 jets. I really dont know why so many guys hate power valves. Putting the right one in goes a long way. Unless you like the way you load up at idle and burn your eyes when you take them out.
 

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Cantard
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Not trying to rant at you so sorry but I see way to many guys blaming the power valve that they just destroyed. Poor timing curves, idle circuts exc. are what kill these things.
 

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Resident Ford Nut
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10,075 Posts
On the dyno I have used 6-8 jet sizes as the equivilent(sp), so 8 is a good benchmark to start with. Power valves arent a bad idea, if it runs fine with it I'd leave it in.

Sleeper CP :D
 

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northern member
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602 Posts
power valves are great in cars or easy planing boats that you want to lean the mixture at part throttle to reduce your fuel consumption . you need to run a higher # pv. (8.5 - 10.5) with a blower because the blower creates a higher vacuum under the carb at a given rpm than if it wasn't there. this is especially true with small dual carb or single carb on a blower because of the increased restriction will create a high vacuum under the carb into the higher rpm (load) range where you need them to open and richen the mixture . you need to check your carb vacuum at your light load cruise rpm and run a pv # the next size down so it opens as soon as you gain rpm and load on the engine . with small carbs you may still have vacuum under them at wot with a blower .
 

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I am going to dump the pv on my 800 holley. The motor is a 454 mag ho with a weiand 177 blower. I have heard that you pull the pv and you must go up in jets. If I do so, how many jet sizes do I go up? Do you have to run the PV on a blower motor? Any info is greatly appreciated :)

Spitter
IMO. The power valve works off the vacuum that the motor produces. Then comes the addition of a blower. BLOWER being the key word here. If you are going to forced induction where in the flying flock does vacuum come into the equasion. If you look at the orofice in a power valve and where it lives in the carb you will find that it really can be without exsistence. As I had stated earlier in the soup, I have taken them out many times and stepped up on the jets only 2 steps and found all acts the same at cruise or idle or wfo. Live and learn,That's my thoughts. M
 

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northern member
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602 Posts
ol guy have you ever put a vacuum gauge on a carb that was on top of a blower ?
 

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Resident Ford Nut
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IMO. , I have taken them out many times and stepped up on the jets only 2 steps and found all acts the same at cruise or idle or wfo. Live and learn,That's my thoughts. M
Not on the dyno, I have done it 3 times ended up 6-8 sizes to balance out and have A/F ratio the same and the same EGT.

He should put a vac guage on it and get a reading.

Sleeper CP :D
 

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E-7 Sheepdog (ret)
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6,834 Posts
When I tried out the no PV "improvement", I wound up 6 jet sizes up, with a huge "hole" on the bottom end that I was now goint to spend all summer trying to fix with accel pumps, squirters, air bleeds, etc, and decided then and here to use a system someone else spent huge ammounts of R&D on, and put it back teh way it was befiore I decided to "fix" it.


Good luck 396.
 

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Lurker
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IMO. The power valve works off the vacuum that the motor produces. Then comes the addition of a blower. BLOWER being the key word here. If you are going to forced induction where in the flying flock does vacuum come into the equasion.
Unless it is a "Blow-Through" system, there is going to be vacuum (depresion) under that carb regardless. If not, that carb will not work as it's operation is dependant on pressure differential (atmospheric/float bowl vs. the venturi/booster) ie. Vacuum/Depresion.
I have little to no blower experiance so...am I missing something??:)sphss

If you look at the orofice in a power valve and where it lives in the carb you will find that it really can be without exsistence. As I had stated earlier in the soup, I have taken them out many times and stepped up on the jets only 2 steps and found all acts the same at cruise or idle or wfo. Live and learn,That's my thoughts. M
How many jets you have to add is mostly dependant (a couple of other small factors also) on the Power valve restriction size (diameter of the orifice that feeds the main well). If you had success going up only 2 jets after removing the PV's, either you ended up WAY lean, or the main system was in left field to begin with.
IMHO
 

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Unless it is a "Blow-Through" system, there is going to be vacuum (depresion) under that carb regardless. If not, that carb will not work as it's operation is dependant on pressure differential (atmospheric/float bowl vs. the venturi/booster) ie. Vacuum/Depresion.
I have little to no blower experiance so...am I missing something??:)sphss



How many jets you have to add is mostly dependant (a couple of other small factors also) on the Power valve restriction size (diameter of the orifice that feeds the main well). If you had success going up only 2 jets after removing the PV's, either you ended up WAY lean, or the main system was in left field to begin with.
IMHO
In the cases where I have ditched the p/v s Neither Fat prior or lean after was the case. I live and breath on reading plugs to see how the combustion chamber temp is doing. M
 

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What happens if you boost reference the power valve. I am runnin an 871 on a 540 w/850 carbs, no power valve in the secondaries. Jetting from the factory was 88 primaries and 96 secondaries, ran way rich. Dropped to 86 front/93 back. Runs better but I am thinking about putting a power valve in the back and going square on the jets.
 

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Highaboosta
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In the cases where I have ditched the p/v s Neither Fat prior or lean after was the case. I live and breath on reading plugs to see how the combustion chamber temp is doing. M
So, you are saying removing the power valves had little to no effect on air fuel ratio???

I need some of what you are smokin'!!! :)sphss
 

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northern member
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602 Posts
pv vacuum

396 where are you ? with your weiand 177 holley 800 set-up i'm guessing your not racing fulltime with it. if you do any amount of cruising and would like to save alot of gas i think you should kept the pv in , no reason not to . you just have to be sure that it has opened by the time that your starting to get into it or your secondaries are starting to open or your manifold vacuum is close to zero and for sure before you see any boost . you need to realize that what your manifold reading is will not be what your carb base is seeing which is where the pv gets it's signal from .
 

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So, you are saying removing the power valves had little to no effect on air fuel ratio???

I need some of what you are smokin'!!! :)sphss
Where the flock did you come up with that shot. I already stated stepped-up on jets... Kool milds want one. M
 

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Lurker
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Where the flock did you come up with that shot. I already stated stepped-up on jets... Kool milds want one. M
Wasn't a shot. :D

Earlier you stated that you only "stepped up" 2 jet sizes when removing power valves. That is HIGHLY unlikely (read impossible unless the enrichment circuit wasn't working in the first place and was tuned as such already) unless the main system was WAY rich to begin with. I mentioned the only way that was possible is if the main circuit too fat to begin with.
Just don't want peeps to think that it is ok to just go up 2 jet sizes when removing power valves if their AFR is proper to begin with. If they are making good power it is quite possible they could hurt somethng before realizing it is 5-7 jets leaner than they started..............thats all!! ;)
 
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