gt40p compresion? and power adders?

Discussion in '1994 - 1995 Specific Tech' started by 94gtslow, Jan 7, 2004.


  1. 94gtslow

    94gtslow Founding Member

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    I was just wondering what the compresion is with gt40p heads. The reason I am asking is that I want to get the Nx wet kit 100-150 shot. But I was thinking of gettring a blower, but i really want the nitrous for better drivablity.

    I heard that is like 9.2.1

    But I am still debating the blower vs n20 , maybe someone can help me decide.


    Mods are in sig
  2. Joes95GT

    Joes95GT New Member

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    The stock compression is 9.0:1. The more cc's a cylinder head has, the LOWER the compression is. The fewer cc's it has, the HIGHER the compression is. I believe the stock heads are 60 or 61cc, and I think the GT40P's are like 62.5cc or something crazy. Therefore, your compression will be lowered to like 8.9:1 or something. Nothing you are going to be able to notice, but it does get lowered slightly.

    The question is what do you want your car to be? If you want a street car that will never see track duty, I would get the blower. Who really uses nitrous on the street that much? If you take your car to the track quite a bit, then I would get nitrous. Driveability is going to be determined by the tune of the car, not what is done to the car. You can have a daily driver with a blower, as some of these guys do, however you have to get it dyno tuned and a custom burned chip is a perfect way to finely tune the driveability and safety of the motor.

    Joe
  3. FastmanGT

    FastmanGT Founding Member

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    No, stock has something like 67cc, the 40Ps are ~58cc

    Your compression will end up about 9.5:1
  4. 94gtslow

    94gtslow Founding Member

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    Ok so its 9.5.1. The head have not been milled, just bolw blended gasket matched and the exhaust cleaned up.

    I just want to know because I was going to get the Nx kit but it the compresion is low I might consider justwaiting and getting a blower.

    I just need to know what it is
  5. Joes95GT

    Joes95GT New Member

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    Whoever told you that is 100% wrong. I don't think there is a SBF head made with 67cc's. There is a variance between combustion chamber sizes on E7's. I've mostly heard of 58-60cc and GT40P's are like 60.5 or 62.5, I could swear they are bigger. Either way, even if the P's are smaller, that slight change in compression will do nothing. We'll say the compression is 9.0 +/- 0.1.

    Joe
  6. FastmanGT

    FastmanGT Founding Member

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    http://www.themustang-net.com/tech_articles/gt40p.shtml

    Cliffnotes: GT40Ps have a 59cc chamber
    E7TEs have ~63.5cc chamber
    My Guesstimates were off, sorry :p

    Half the reason the Ps perform better than the regular GT40s is the increase in compression.
  7. twotonefreak

    twotonefreak New Member

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    I will post up this weekend how my friends 88 GT with P heads, mass air conversion and Novi 2000 runs.

    Fast man where your numbers with all the mods in your sig?
  8. FastmanGT

    FastmanGT Founding Member

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    The dyno was with heads, intake, full exhuast, homemade cai, and gears. At the time, the converter was shot and the tranny was slipping. I will get a dyno and air/fuel with all the new bolt-ons and some underdrives once the tranny is back in the car and a few other mods are complete.
  9. fiveotony

    fiveotony Founding Member

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    I have P heads the reason why they have more hp is the valve sizes and chamber size not compression. I have milled mine .020 for some more compression but it only netted me just a touch more. they are stock compression heads off a explorer v-8.

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