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Thread: Upping the boost on my 8-71 blown big block

  1. #1

    Upping the boost on my 8-71 blown big block

    Here's the set up. 468 BBC. 8-71 with 2 750's. Jetted square with 72's. 8 to 1 pistons. 61 top pulley, 54 bottom, for about 9% under-driven. Runs on 93 octane pump gas. Chassis dyno'd at 461 hp, 420 ftlb tq. I'd like to kick up the boost, without having to go to race gas. I figure swapping the pulleys would be way too much, even jetting up the carbs. So, what size top pulley can I go to? And how much higher on the jets?

  2. #2
    Senior Member RACING JUNKIE
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    Something is big time wrong, those dyno numbers are too low.
    JMO
    Dave
    http://www.racingjunk.com/profile/343797
    "All that is necessary for the triump of evil is for good men to do nothing" Edmund Burke

  3. #3

    Upping the boost on my 8-71

    I thought so too. It was on a portable chassis dyno at a car show, so who knows how accurate?

  4. #4
    Senior Member RACING JUNKIE
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    Do you have a boost gage? Is the blower teflon stripped?

    You can probably get away with 1 to 1 ratio with 93 octane but i wouldn't think any more than that.

    JMO

    Zip.

  5. #5
    Thanks for the response!

  6. #6

    Upping the boost on my 8-71 blown big block

    Is there any "rule of thumb" as far as jetting increase, when changing pulleys from 54-61 (9% under) to 54-54 (1 to 1)? Like, maybe, one jet size per two teeth or something? Just some sort of starting point, so I don't melt pistons trying to find the right combo!

  7. #7
    Senior Member RACING JUNKIE
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    Re: Upping the boost on my 8-71 blown big block

    Quote Originally Posted by f35rocket
    Is there any "rule of thumb" as far as jetting increase, when changing pulleys from 54-61 (9% under) to 54-54 (1 to 1)? Like, maybe, one jet size per two teeth or something? Just some sort of starting point, so I don't melt pistons trying to find the right combo!
    Never heard of a "Formula" like that . . It's just "More air . . More Fuel".

    Start with jetting that should put you rich and then lean it out to taste . . Kinda like making Chile . . .

  8. Racing Junk


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