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  1. #1
    West Texas RXP skoepp's Avatar
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    comparing 8.4:1 and 9.5:1 pistons

    I would like the thread to give real world data, facts, opinions rather good or bad.
    Looking for information on setups, both SC and Turbo.

    If anyone has good knowledge and seat time between the different comp regarding to tuning, performance differences gained or loss.

    Is it possible the higher comp creates more issues with cavitation ?

    How are the 9.5:1 setups working with highboost and standalone ecu?

    Open to full discussion.


  2. #2
    Stockrxp's Avatar
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    you know my opinion

  3. #3
    R88ory RXP's Avatar
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    Yes Higher comp makes it more difficult to eliminate cavitation out of the hole.

    Depending on boost level you dont need a standalone. If you want to run big boost with the higher comp then IMO it would be benificial to have the control of a SA ignition.

    Fueling is not much of an issue, there are many ways of dealing with the motors demands without needing a SA but its the timing or fact you going to be running less of it that comes into play. One thing to consider, If your stock remapped ECU has knock sensing, it will help to try and keep the motor safe but if your ECU is pulling timing due to knock, your losing power and are effectively badly tuned.

    Good Luck R88

  4. #4
    West Texas RXP skoepp's Avatar
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    I will be running GH vtech reflash to run 60 psi injector and approximately 18 psi.
    I am not sure if the OEM 04 knock sensor will be needed, I assume it does?
    Rev limter will be set somewhere below 9000 rpm to try to tune for 8800 rpm.
    I will be using 2 rude or 3 rude.

    The cavitation does concern me if there is no good way to tame it.

  5. #5
    R88ory RXP's Avatar
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    2Rude levels of boost should not cause you problems but its all in the map really.

    If Jerry has a map that is tuned for higher comp or can tune one then thats what you would want.

    Im assuming the Vtech uses the knock sensor??? If so then thats gona help stop DET from happening.

    Your also at altitude which means you can get away with things that people at sea level would have issues with. For instance, I would have been very tetchy about running a 3rude or any other charger of that level on 9.5 pistons with a re-mapped ECU but StockRXP was and was making enough power to kill a shaft, ok there are many factors to why a shaft breaks but power is a big one. In some respects your lucky coz your location builds in a bit of safety, but on the otherside you need more mods to make the same power as somebody at sea level.

    R88

  6. #6
    Duke's Avatar
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    Personaly I would never run anything less then 9.5. May have to pay attention to AF and timing might be an issue if you fuel is questionable. It does take some added work to make it hook up but man is it worth it.

  7. #7
    blackvr's Avatar
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    high comp = blown headgasket on a rec boat wit anything over 15 psi imo

  8. #8
    West Texas RXP skoepp's Avatar
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    Thanks for the replys, that is what I was hoping for those with experience.
    TTT

  9. #9
    Stockrxp's Avatar
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    Looks like with a 3 rude you can't run those 9.5s at your rpms

  10. #10
    Orlando Shark's Avatar
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    Quote Originally Posted by blackvr View Post
    high comp = blown headgasket on a rec boat wit anything over 15 psi imo
    I don't agree with this comment. As long as you torque your head correctly and keep your afr's under 12's you will be fine.

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