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Thread: blown bbc tune up help

  1. #1

    blown bbc tune up help

    i purchased a 496 bbc, 871 blower, 680 lift cam 112 lobe center, bird hat, msd dist and 7al3, hilborn 150 pump, gear drive, 291 casting steel heads, hat nozzles only. lookin for help with timing, nozzle sizes, main and bypass jets, etc. thanks for the help. the guy i bought the motor from over the winter said he'd send me the tune up info and never has. so any help would be appreciated.

  2. #2
    Senior Member RACING JUNKIE
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    Without having the pump flowed, it's a shot in the dark.
    -WJ Birmingham

    OneBadGMC.com

  3. #3
    pump is new out of the box, don't know if that helps or not.

  4. #4
    Senior Member RACING JUNKIE
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    OK, then what are the numbers on the flow tag?
    -WJ Birmingham

    OneBadGMC.com

  5. #5
    pump rpm 1500 2.207 gpm, 3000 rpm 4.904 gpm, 4000 rpm 6.539 gpm.

  6. #6
    Senior Member RACING JUNKIE
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    Is this a gasoline setup? I sure the heck hope it's not alky.

    If it is alky, you need 2 things.

    1. A bigger pump... something in the 8-10 GPM range.

    2. A better ignition, that 7AL aint gonna cut it.

    Now, if you're just wanting something to play with on the street and look cool, you can under drive the blower and make what you have work.

    If you want to race, and make some decent power, that pump and ignition has to go.

    If you want to talk directly about this, PM me your ph#.
    -WJ Birmingham

    OneBadGMC.com

  7. #7
    Senior Member RACING JUNKIE
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    Here, just some quick numbers...

    If you ran 8 flowed .043 nozzles in the hat...

    That would give a system pressure of about 185 PSI (you really want 150-200 PSI for good response).

    The blower would have to be run at 13% under driven.

    The return jet would be between a blank and .012

    Boost, with a typical 8-71 on that big of a motor would be just under 8 PSI.

    HP would be in the 750 range.

    That is assuming about 9:1 static compression.
    -WJ Birmingham

    OneBadGMC.com


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