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Thread: Rear Power valve and other question

  1. #1
    Join Date
    Jun 2010
    Location
    Jamestown, NY
    Posts
    7

    Default Rear Power valve and other question

    Hey all, im new to this forum hopefully i can get some answers ive been searching for... well i have a small block in my 85 s10 setup as 350 .060 over flat tops, comp XE 274 cam, EDEL RPM intake,Aluminum 190cc 64cc chamber heads,3000 stall TH350 with 3.73s in the rear... im running an older HP Double pumper 750 right now and just have a few questions... one for the street im running a powervalve in the back a 6.5 im currently jetted at 72 front and 73 rear with both PV 6.5.. I was just wondering if there would be any benefit to not running a rear PV and jetting up the rear, or possibly running a smaller PV.. i pull about 14HG in drive of vacuum... it seems to run good but maybe a tad rich... my other question is the secondary linkage on the carb.. is there a way to shorten the linkage so the secondaries open earlier? my pedal seems to run out when i get into the 4barrel and ive shortend the cable as far as i can... ANY help or advice would be greatly appreciated here... Thanks

  2. #2

    Default

    two power valves on a street driven car are unnecessary, imho. You are dumping gas every time the vacuum drops, even if the secopndaries are not open.

    I would not bend the linkage. Then your sencondaries will open too soon. Either get a different cable or take the car to someone who has the expertise to modify the existing cable.

    Z.

    '66 GT-350 Original Drivetrain, Sheet-Metal, Interior, & Paint

  3. #3
    Join Date
    Mar 2010
    Posts
    23

    Default

    Quote Originally Posted by zray View Post
    You are dumping gas every time the vacuum drops, even if the secondaries are not open.Z.
    ??? Are you referring to the accelerator pumps? Cause if anything else is 'dumping gas' it's time for a rebuild kit.
    If you move the cable attachment point down (closer to the throttle shaft) you will gain some travel. From the 1/2 inch hole to the 1/4 inch hole.
    This site sure could use some actual Holley tech people. Lots of misunderstanding could be fixed.

  4. #4

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    every time the vaccumn drops , the power valve(s) will dump fuel into the main well. Even with the (secondary) throttle plates barely cracked open, the extra fuel in the main well will be drawn into the venturi. No street engine needs two power valves, & I doubt any Holley tech rep would make a case otherwise.

    '66 GT-350 Original Drivetrain, Sheet-Metal, Interior, & Paint

  5. #5
    Join Date
    Mar 2010
    Posts
    23

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    Ever hear of a water level? What makes you think the main well isn't filled to float level at idle? Even the small amount of fuel being sucked out of the main well by the IFRs is quickly replaced by the main jets. Once the main circuit starts and the air bleeds become effective the main well gets frothy. Then the open power valve can have an affect. Before that the power valve has no effect. Try it yourself. Jet up 8 sizes and see if the car still idles. Don't have jets 8 sizes bigger? Take them out completely and try it. Secondary power valves can be helpful on expressway ramps (or road courses) when you're giving heavy throttle to keep the RPMs up but you're not loading the motor much. In those (admittedly rare) conditions you don't need or want full power enrichment so a secondary power valve will give a crisper throttle and keep the plugs cleaner. They can be uncovered under drag race conditions with sticky tires so that is the only time they should be removed. Why do you suppose Holley put them in the carb in the first place?

  6. #6

    Default

    first of all, if I insulted you ,or your intelligence, I offer my apologies. People may reasonably disagree without getting personal.

    The OP is having problems with street driving. His carb was never meant to be used on the street. He can make it more street friendly by removing the secondary power valve, and increasing the size of the secondary main jets. Any Holley rep will suggest the same thing.

    '66 GT-350 Original Drivetrain, Sheet-Metal, Interior, & Paint

  7. #7
    Join Date
    Mar 2010
    Posts
    23

    Default

    My reply was in no way personal. Not sure why you would think that. I'm not sure what is so un-street friendly about a power valve. If someone drives on the street they use all power levels of their motor, not just idle and wide open. Street and road course use are very similar. If someone drives around with a vacuum gage and a throttle position sensor they might find instances where the secondaries are feeding fuel but the vacuum level ( and the requested power level) does not require full secondary enrichment. Picture a stick shift small block cranking around an on-ramp at 4500 RPM in 3rd gear. Not wide open but the secondaries are open 10-15 degrees. That is what a secondary power valve is for. I can't think of any street situation where a secondary power valve is undesirable.

  8. #8

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    Well, I just have to agree that we disagree. My only rebuttal would be a question; if having a secondary power valve is so desirable on a street driven car, why does Holley not offer them on all street double pumper carbs?

    I'm not not great at searching Holley's web site, so it's likely I'm overlooking something, but I can't find them offering any secondary power valve equipped street, or street/strip, carb.

    '66 GT-350 Original Drivetrain, Sheet-Metal, Interior, & Paint

  9. #9
    Join Date
    Mar 2010
    Posts
    23

    Default

    Not sure if Holley makes a 'street" double pumper carb. But the original 3310 vac sec street carb that Chevy put on it's hi-po models (302 small block and 396 big block) had both primary and secondary power valves. Quite a few other carbs have them too. http://www.holley.com/data/TechServi...%20Listing.pdf What purpose do they serve?

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