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Max. c/r on 91 octane?

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    Max. c/r on 91 octane?

    Just wondering:
    What is the maximum compression that I should run using 91 octane, and stock chip on a 2.7 stroker?
    Thanks in advance.

    #2
    how much timing advance is the key...
    Tenured Automotive Service Professional - Avid BMW Enthusiast

    Vapor Honing & E30 ABS Pump Refurbishment Service
    https://mtechniqueabs.com/

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      #3
      Isn't the timing determined by the ecu?
      Sorry for the dumb question, I don't know very much (nothing) about timing! :?

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        #4
        Yes but you can buy an adjustable cam gear and change it yourself, or alter the sensor ont he front of the crank a little
        85 325e 2.7 ITB'd stroker

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          #5
          Well, assuming that I dont have an adj. gear and haven't moved any sensors.

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            #6
            9.5:1
            Tenured Automotive Service Professional - Avid BMW Enthusiast

            Vapor Honing & E30 ABS Pump Refurbishment Service
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              #7
              Well I'm planning on putting early euro eta pistons, and eta crank into the m20b25. And doing this will give me about a 10.1:1 c/r (from what I've been told).
              Any suggestions on what to do? Slighty thicker head gasket maybe?
              94 octane is the highest I can get, and it's not extremely common. I dont really want to have to resort to octane boosters, etc.

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                #8
                Originally posted by Jordan
                9.5:1
                Bingo.

                '86 325 2.8i stroker - Arctic Blue
                '11 328i Sports Wagon - LeMans Blue
                Strictly Eta

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                  #9
                  Are oversize head gaskets available, and will they be able to lower the compression to the 9.5:1 that you suggest?
                  I can only seem to find +0.3mm gaskets, and that doesn't seem like a substantial amount.

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                    #10
                    Even 9.5 is a little much as gas gets worse and worse.
                    Adam Fogg- '88 M3

                    Common sense- It's the new 'gifted'

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                      #11
                      Originally posted by AdamF 88iS
                      Even 9.5 is a little much as gas gets worse and worse.
                      True. Its just owl piss nowadays.

                      Jon
                      Rides...
                      1991 325i - sold :(
                      2004 2WD Frontier King Cab

                      RIP #17 Jules Bianchi

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                        #12
                        Originally posted by ryan_george
                        Are oversize head gaskets available, and will they be able to lower the compression to the 9.5:1 that you suggest?
                        I can only seem to find +0.3mm gaskets, and that doesn't seem like a substantial amount.
                        ^^^^^^

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                          #13
                          Comp .

                          Hey Ryan ,
                          dont listen to me , but My Chevy Camaro is Running 10.5:1 on 91 octane at 36 degrees total advance .

                          I dont know what it would be for the e30
                          But on my E30 im going with ROSS pistons 10.0:1

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                            #14
                            stock compression is 8.8:1, and with a stock timing/fuel chip you should be able to get away with 10 c/r if you run 93 premium or even 91. I was running 9psi on stock compression, stock ignition, without detonation, and that is like running over 10c/r.

                            Also, Who here has actually tested fuel to prove that it's any worse than it used to be, haha, it's not, because they have to meet that minimum octane rating to sell the shit.

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                              #15
                              Thanks for the input guys. :D

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