CR to use for a daily driver?

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  • Ross
    S2Forum Possessed
    • Aug 2005
    • 3399
    • Country: England

    #1

    CR to use for a daily driver?

    Just wondering what the general outtake is - I've read lots about compression ratio's, and the effect they have, but to what magnitude.

    Scenario: you're doing an RS2 conversion, want to maintain reasonable round town off-boost driveability without sucking the tank dry every other day, yet want to get the most of the performace... where's the comprimise?

    My current understanding is, that the car is 9.3 stock; the metal HG is 9.0 but the 'hybrid' jobs take it down to 8.5 or lower! I am thinking the 9.0 with a metal HG is probably a good comprimise (is this what the RS2 uses?); however I don't know if it's gonna make a huge difference to top-end. Are we talking a matter of a huge drop in off-boost driveability for a few extra horses.

    Would definitely like to hear some expert opinions on this, I've tried to digest the technical threads but I still don't understand how much of an impact it can have! And this decision needs to be make pretty soon

    Cheers
    Ross
    AUDI - saving Dad's from minivans since 1994
  • Greg_S
    Administrator
    • Jul 2003
    • 12430
    • Country: United Kingdom

    #2
    Tom should be able to give you some good feedback on this one. His car has the compression lowered quite a bit. Personally I wouldnt if it is a daily driver
    Greg

    S2Forum.com Administrator & Webmaster

    '93 Coupe with a few tweeks

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    • volcano rs
      S2Forum Fiend
      • Jun 2005
      • 2265
      • Country: United Kingdom

      #3
      unless you are going over say 400 bhp i wouldn't bother even then i don't think you need to

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      • SteveH
        Super Moderator
        • Jul 2003
        • 4460
        • Country: United Kingdom

        #4
        Keep the compression ratio standard and add water injection. It's only under high boost conditions that the CR will cause problems with detonation. Water injection will reduce the likelyhood of this happening. Then you get the benefits of running a higher CR under normal driving conditions, so it wont feel flat off boost.
        91 Modded 3B
        14 A6 Avant Black Edition

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        • volcano rs
          S2Forum Fiend
          • Jun 2005
          • 2265
          • Country: United Kingdom

          #5
          Originally posted by SteveH
          Keep the compression ratio standard and add water injection. It's only under high boost conditions that the CR will cause problems with detonation. Water injection will reduce the likelyhood of this happening. Then you get the benefits of running a higher CR under normal driving conditions, so it wont feel flat off boost.
          your thinking is like mine

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          • Ross
            S2Forum Possessed
            • Aug 2005
            • 3399
            • Country: England

            #6
            Thaks guys. I shall probably go with the metal head gasket, which I understand lowers it very slightly. But I think I'll miss on the hybrid gasket to maintain a bit more driveability. Even if it means it can't me mapped quite so aggressively. Will talk to Tom today...
            AUDI - saving Dad's from minivans since 1994

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            • mcandmar
              S2Forum Zealot
              • Apr 2004
              • 5118
              • Country: Ireland

              #7
              Ross, thats the conclusion i came to with my build. Dont forget if your doing a full rebuild your probobly going to get the block and head shimmed so thats going to put it back up slightly. Dont ask me how much, cant work that out off the top of my head.
              91CQ20v - Gone to a new home
              93UR-S4 - The Magic Carpet
              94S2Bus - The Emerald Express

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              • MarkPS
                S2Forum Fanatic
                • May 2005
                • 65
                • Country: England

                #8
                Hi

                Look at this article an a 428bhp MTM S2 http://www.aoqe47.dsl.pipex.com/images/RSR_02.jpg

                Esp the bit regarding increasing the CR from 9 to 9.3. assuming the article is accurate.

                Page 1 http://www.aoqe47.dsl.pipex.com/images/RSR_01.jpg
                Page 3 http://www.aoqe47.dsl.pipex.com/images/RSR_03.jpg
                Page 4 http://www.aoqe47.dsl.pipex.com/images/RSR_04.jpg

                Regards
                Mark
                88 URQ

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