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Thread: Compression ratio suggestions for a E85/6262/daily driver

  1. #1
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    Default Compression ratio suggestions for a E85/6262/daily driver

    Im putting a 6262 custom kit in my car this week and am still on the stock motor(motor has 15k miles on it). I have driven a car with the same kit on it and its damn laggy obviously but I love the top end. Im looking to start piecing together the internals for a bottom end for it and am wondering what CR I should go with? I only run E85, the cams I have now are the kelford 272's(its a VIII) and the 6262 is on the larger .84 hotside. I would like to get it to spool a bit better then it does on my friends car thats running about 8.0-8.4:1CR and kelford 272/280 combo on his IX.

    My options Im thinking is a couple things.... 10:1 and run the smaller .64 hotside, 10.5:1 run the smaller hotside but go to larger cams or just a kelford 272/280, 11:1 and run the larger hotside????? Just trying to get a game plan down so any inpu would be real helpful... TIA

  2. #2
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    The compression change makes the car feel a bit better off boost but will not actually make the turbo spool faster. I've done back to back testing of this and the boost still seems to hit about the same as it did before, so if the turbo makes 20 psi at 5000 rpm on that turbo on a 8.5:1 engine, on a 10.5:1 engine it is going to make the same 20 psi about the same spot.

    If you want the turbo to spool faster there are a few things you can do.

    1. Larger displacement, like a stroker, which will limit you to 8500 rpm
    2. Smaller turbine housing, which will cost you power up top.
    3. Smaller primary header turbo, which will cost you power up top at some point.
    4. Stock intake/throttle body helps.

    What I'd suggest is if you want a fun to drive fast car you should build the car with either the Red or Black, chances are if you build the car right you will be able to beat most big turbo'd EVO's anyway.
    David Buschur
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  3. #3
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    Thanks for the response Dave. I guess I should be a bit more clear on my expectations. I'm not overly worried about spool really. More like drivability. Right now the turbo is on a 2.0L with low compression(8:1) and it's semi annoying to drive light to light etc... I'm not concerned where the power is really as when I need it I can just down shift etc etc. I have a fair amount of friends with semi fast v8's and single turbo supras. I tend to have a bit of fun from a roll and would eventually like to see the car run a 9sec pass... I just don't want to have to hit boost to drive it around town.

  4. #4
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    10:1 sissy. Bryan and I already said that. Just do it. :P


    You'll never get away with 10.5:1 on our 91 oct even as an emergency fuel.
    Last edited by lqdchkn; 03-09-2010 at 11:20 PM.

  5. #5
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    SR is getting a e85 pump so F 91 all together... Planning to never touch the garbage again.

  6. #6
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    David, what kind of limits have you seen with boost vs. compression on different fuels?

    For example,maximum boost (or torque?) on 91 octane and 10:1.
    E85 and 10:1
    E70 and 10:1

    I know it's a "loaded" question and will be highly sensitive to setup. Just curious what you've been able to get away with for compression on lower octane fuels?

  7. #7
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    I would be real interested to hear some general feedback on that as well. Also in terms of motor life would it be easier on the motor say running 11:1 and 30psi, or 10:1 and 35+psi? Basically whats going to wear internals faster, boost or compression?

  8. #8
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    The best thing about building a higher compression engine is you will improve your efficiency off boost, and thus you will have better fuel economy than a low compression engine on E-85. Since you are not doing this for fuel economy reasons I have no idea what would be best for you though.... I personally am always a fan of higher displacement engines.

    Keith

  9. #9
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    It is a daily driver though so fuel economy would be VERY VERY welcomed... Particularly since its on e85. The reason I Im not set on doing more displacement is two things.. one being cost and two being the lack of rev capability. I would like to put the bottom end together once and eventually when I get a built head and a couple other things on it crank the boost and click a 9sec pass out of it. The plan is to do a crower rod/je piston setup and throw the stock head on there for the time being and then do a BR st3 head, intake and a big TB next fall and run a few passes in it.
    Last edited by Stevo8; 03-10-2010 at 02:40 AM.

  10. #10
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    I went from 9-1 to 10-1 in my saab aero daily driver and gained 5+ mpg! (25to30.4+)Only differance was compression. It has more pop but boost was the same.

  11. #11
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    I see no difference in wear when I take apart a low compression engine vs a high compression engine. Tuning, overall HP and RPM are what generally ruin an engine.

    I have not done any MPG testing on low vs high compression on the same CC engines.
    David Buschur
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    Bad Bish, 9.04@159.64
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  12. #12
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    Thanks Dave. I think I'm going to go with a 10-10.5:1 setup

  13. #13
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    Still voting for 10 over 10.5. Even though E85 is fantastic fuel at 10.5 you may have to run less timing from increased cylinder pressures. I don't really know though since I have no experience or haven't really seen any articles on high compression E85 motors. 10:1 just seems like it would be a happy medium allowing for still somewhat agressive timing advance.

  14. #14
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    For reference, most of our pistons have gone to a "10:1" design. I say this because obviously depending on the CC of the head, head gasket etc. that number will vary by a little. I've run as high as 11.5:1 on pump gas and 30+ psi of boost in quite a few enginees, no problems.
    David Buschur
    www.buschurracing.com

    COBB TUNING DEALER AND PRO TUNER

    BUSCHUR RACING on FACEBOOK

    BUSCHUR RACING DSM/EVO SHOOTOUT on FACEBOOK

    OFFICIAL DSM/EVO/GTR SHOOTOUT INFORMATION

    First 4g63 in the 12's, 11's, 10's, 9's, 8's and 7's.
    WORLD'S FIRST EVO8 IN THE 8'S
    WORLD'S First EVO in the 9's on pump gas.
    2011 NASA Championships TTD runner-up

    Bad Bish, 9.04@159.64
    Project White, E85, 10.35@138.53 mph, ECUFLASH TUNED

  15. #15
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    So in theory 10.5:1 on a 6262 with .82 hotside should do just fine? Also if running your stg3 head, what headgasket would you recommend and roughly what will that hg effect the CR?

  16. #16
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    I'd recommend the stock EVO8 head gasket for 8's and stock EVO9 for 9's.
    David Buschur
    www.buschurracing.com

    COBB TUNING DEALER AND PRO TUNER

    BUSCHUR RACING on FACEBOOK

    BUSCHUR RACING DSM/EVO SHOOTOUT on FACEBOOK

    OFFICIAL DSM/EVO/GTR SHOOTOUT INFORMATION

    First 4g63 in the 12's, 11's, 10's, 9's, 8's and 7's.
    WORLD'S FIRST EVO8 IN THE 8'S
    WORLD'S First EVO in the 9's on pump gas.
    2011 NASA Championships TTD runner-up

    Bad Bish, 9.04@159.64
    Project White, E85, 10.35@138.53 mph, ECUFLASH TUNED

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