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Thread: High Compression & Pump Gas??

  1. #1

    High Compression & Pump Gas??

    I've been told many times that a high compression engine (12-13:1) can be driven on pump gas as long as it does not have a heavy load on it, i.e. it's just driven normally down the street. I'm planning a 13:1 BBC project with aluminum heads and now I'm wondering if there is any truth to this? Also, if this is true what would be the max dynamic compression ratio or cranking psi, I should aim for so if I had to drive it on pump gas for a few miles it would be ok. Thanks

  2. #2
    Administrator RACING JUNKIE bjuice's Avatar
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    NOT TRUE......
    12:13 to 1 you better have race gas,,,or you will detonate and kill it.
    Bjuice..

    "I'M YOUR HUCKLEBERRY ! "

  3. #3
    Member JUNIOR BUILDER
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    bjuice is right - that thing's gonna hammer even under the lightest acceleration. And of course pump gas ain't what it used to be..... 8) JB

  4. #4
    Senior Member MASTER BUILDER
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    I agree with everyting said above. why do you want high compression if your not going to use it?

    if you just want that little extra at the track, you can use pump gas compression (9 or 10-1 comp) and throw some nitrous at it to bring it up to the race track performance that you want.
    1987 Pontiac Fiero GT
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  5. #5
    Senior Member DYNO OPERATOR
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    The problem is not if it can do full throttle acceleration. The problem is when trying to do small part throttle acceleration at lower rpms like as in normal driving.

    I am a big compression on the street freak, but this is beyond me with current available pump gasolines. I would be scared to build it knowing this.

    If this is what you are determined to do, I strongly suggest to use E-85 Fuel which is available in some places at the pump.

    Also follow Big Joe's advice about killing it in gear with foot on the brake.

    Ed
    " Let all things that hath breath, praise the Lord. Praise Ye the Lord" Psalms 150 vs 6.

  6. #6

    pump gas !!

    If your max DCR is over 8.75.. I sure would not try and run any
    pump gas!! :cry:

  7. #7
    Thanks everyone, I was planning to run race fuel all the time but it's a streetcar and I was worried that I might want to drive it futher than my fuel cell would allow. I think I'm going to lower the compression to 11 - 11.5:1 and run a good head so I can have the best of both worlds. The combo is gonna be a BBC 496 (4.31x4.25), 11 - 11.5:1, 280/284@50 .722"/.722" cam. I think that cam will put me around 175psi cranking with 11.5:1 static. What heads would you reccomend for best performance and will this be ok for pumpgas?

  8. #8
    Administrator RACING JUNKIE bjuice's Avatar
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    your still too border line for pump gas in my book at 11;5;1 ...10:1 max is where i would want to come in...plus you cannot guarantee the quality of fuel you are gettting from the pump ( someone might have mentioned earlier)...

    as far as the heads are concerned..there are many more qualified people to answer this..but what i will say is stay away from any heavy port work with the heads or intake for street use..a good bowl blend is about it..

    Brian
    Bjuice..

    "I'M YOUR HUCKLEBERRY ! "

  9. #9
    Senior Member RACING JUNKIE
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    Quote Originally Posted by bjuice
    your still too border line for pump gas in my book at 11;5;1 ...10:1 max is where i would want to come in...plus you cannot guarantee the quality of fuel you are gettting from the pump ( someone might have mentioned earlier)..

    Brian
    I agree with Brian for sure 11.5 in my book is to high also. I'd go with a Brodix BB2 head if it were mine.
    David Lanning
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  10. #10
    Senior Member EXPERT BUILDER
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    Ya 10:1 maybe 10.5:1 Forged pistons max but check the plugs. Brodix or AFR alum. heads and I would have a real good bottom end so NOS can be added for that "Ka-Pow" factor :wink:
    If a 5 lb hammer can't fix it,it must be electrical
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