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C/R on a m20b25 / somebody please explain ?

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    C/R on a m20b25 / somebody please explain ?

    OK guys heres my question .
    Why do people say that 10.5 compression is too high for the m20b25 on 91 oct. ?

    While my 2001 325ci has 10.5 c/r stock runs on 91 oct.

    #2
    24 vlave head versus 12 valve head, better fuel injection setup, and the list goes on
    85 325e 2.7 ITB'd stroker

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      #3
      Re: C/R on a m20b25 / somebody please explain ?

      Originally posted by robmespeedy
      OK guys heres my question .
      Why do people say that 10.5 compression is too high for the m20b25 on 91 oct. ?

      While my 2001 325ci has 10.5 c/r stock runs on 91 oct.
      Electronics play a big part. That engine also has knock sensors, much more advanced engine control The flow is also a lot better as well as the dual vanos on that engine. M20 ain't got shizzie.

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        #4
        The shape of the M20 combustion chamber is also more prone to hot spots and pinging than the DOHC motors are.
        Adam Fogg- '88 M3

        Common sense- It's the new 'gifted'

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          #5
          do any BMW motors use hemispherical combustion chambers?
          Michael Spiegle

          '01 Ford Escape / Daily Driver
          '99 M3 / Track Car
          '87 325is bronzit / wtf car
          '06 Daytona Triumph 675 / Daily Rider

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            #6
            engines such as the s14 and s38 do hence the spark plugs being in the center of the head.

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              #7
              cam profile and overlap make a HUGE difference in detonation resistance too. C/R is static, actual pumping pressure is far more relevant.
              Luke

              Closing SOON!
              "LAST CHANCE FOR G.A.S." DEAL IS ON NOW

              Luke AT germanaudiospecialties DOT com or text 425-761-6450, or for quickest answers, call me at the shop 360-669-0398

              Thanks for 10 years of fun!

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                #8
                Originally posted by StereoInstaller1
                cam profile and overlap make a HUGE difference in detonation resistance too. C/R is static, actual pumping pressure is far more relevant.
                Luke
                This is true. A very agressive cam lowers the effective compression raito as the motor runs, and can relieve some detonation issues.
                Adam Fogg- '88 M3

                Common sense- It's the new 'gifted'

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