Jets sizes when dumping the PV(Blower Mill)
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Jets sizes when dumping the PV(Blower Mill)

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    B.A.M aka "Black Azz Mike 396_Ways_To_Spit's Avatar
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    Default Jets sizes when dumping the PV(Blower Mill)

    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

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    Quote Originally Posted by 396_Ways_To_Spit View Post
    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 71hallett's Avatar
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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.
    Quote Originally Posted by gn7 View Post
    It would be a balmy 85* in Steel's shop if he would move a little faster

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    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.

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    northern member Canuc's Avatar
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    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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    Senior Member ol guy's Avatar
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    Quote Originally Posted by 396_Ways_To_Spit View Post
    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 Canuc's Avatar
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    ol guy have you ever put a vacuum gauge on a carb that was on top of a blower ?

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    Quote Originally Posted by ol guy View Post
    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.

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    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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    Quote Originally Posted by ol guy View Post
    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??

    Quote Originally Posted by ol guy View Post
    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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    Quote Originally Posted by Warp Speed View Post
    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??



    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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    Familymatters;

    You can always try one of these:
    http://www.predatorcarb.com/performance/carburetor.html

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    Quote Originally Posted by family matters View Post
    wonder when someone is going to make a carb with a jet for the transition ?
    no power valve.. no more rubber to rot out with hot fuel.
    That's been done decades ago.........http://fuelairspark.com/

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