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Found the limits of a stock M20B25 Bottom End

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    #31
    New 2.7 is in and were going to get it tuned this weekend. Wont be going past 25psi for now till we swap in the 2.8 forged stroker. Ill be rolling around on wastegate (10psi) for normal driving, with a highboost button for 25psi.
    - AXIS POWERS - 2JZ E30 Build
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      #32
      First thing I was gonna say was it's your spark cut that probably caused it. M20s are safer to use fuel cut instead. or raise your limiter a bit so you don't have to stand on it.

      likely what happened is you broke a rocker, then had piston/valve contact, which caused the bottom end to fail since it was under so much stress. The pictures of the valves pretty much tell the same story.
      Build thread

      Bimmerlabs

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        #33
        Just had a thought, my launch control is -20 spark cut. I got HD rockers but is it gonna eat shit lol, I've used it a few times now


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          #34
          -20 is a lot, ive been messing around with spark cut for rolling launch control but havent felt safe going past 0 degrees with out it wanting to back fire.

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            #35
            Originally posted by nando View Post
            First thing I was gonna say was it's your spark cut that probably caused it. M20s are safer to use fuel cut instead. or raise your limiter a bit so you don't have to stand on it.

            likely what happened is you broke a rocker, then had piston/valve contact, which caused the bottom end to fail since it was under so much stress. The pictures of the valves pretty much tell the same story.
            No rockers were broken. I was running -5* on spark cut, but now i am spark and fuel cut. I think there was just too much cylinder pressure for the rod to handle. I also am running 20* of timing at max torque and up top so that could very well have a lot to do with it
            - AXIS POWERS - 2JZ E30 Build
            Interested in drifting in the ArkLaTex? Join us!
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              #36
              Hard to tell from your pics.....does offending cylinder walls have lower carbon line than other cylinders? Kind of looks like that in the picture. If so, was your con. rod already bent for a while when this happened?

              Also, any pictures of the crank thrust bearing? too much trust will twist/flex the rod and can crack the rod or cause a mess in the wrist pin area.
              Could be something as simple as too much heat in that cyl (not enough fuel) and as a result locked piston?

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                #37
                Originally posted by SLEEPYDUB View Post
                I also am running 20* of timing at max torque and up top so that could very well have a lot to do with it
                You don't want to see my timing maps then lol. A few of our builds have 23 @ 190kpa and 4300rpm...stock rebuilt bottom ends, 56-62mm compressors, 93 octane (which is actually e10 here). E85 still isn't widespread down here yet.
                john@m20guru.com
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                  #38
                  20 degrees really isn't much for a 2v engine though.
                  Build thread

                  Bimmerlabs

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                    #39
                    Originally posted by nando View Post
                    20 degrees really isn't much for a 2v engine though.
                    At peak TQ and decent boost levels? I often see people pulling too much timing, but 20+ is healthy with a turbo. Go check out the maps thread ;)
                    john@m20guru.com
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                      #40
                      Originally posted by ForcedFirebird View Post
                      You don't want to see my timing maps then lol. A few of our builds have 23 @ 190kpa and 4300rpm...stock rebuilt bottom ends, 56-62mm compressors, 93 octane (which is actually e10 here). E85 still isn't widespread down here yet.
                      Id love to see a good timing map to compare to if you wouldnt mind posting it up. I thought 20* at max torque and higher would be a problem, but apparently it is not according to what you're saying

                      Originally posted by nando View Post
                      20 degrees really isn't much for a 2v engine though.
                      Good to know, I guess I may leave my map alone then. When boost comes on, it hits HARD with the current timing

                      Originally posted by ForcedFirebird View Post
                      At peak TQ and decent boost levels? I often see people pulling too much timing, but 20+ is healthy with a turbo. Go check out the maps thread ;)
                      Do you have any specific maps I should check out? I didnt see any signs of detonation with my engine, just though maybe I was making too much torque for the stock rods to handle.
                      - AXIS POWERS - 2JZ E30 Build
                      Interested in drifting in the ArkLaTex? Join us!
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                        #41
                        I was pointing that comment more towards Chris, people with supposed dyno tunes, even have awful timing maps. Stick to the age old rule and pull 1-2 for every 10kpa (just over 1psi) as a base, then go up from there.

                        For several reasons, I would rather not post my maps, specially an aggressive dyno tune.
                        john@m20guru.com
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                        Transaction feedback: Here, here and here. Thanks :D

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                          #42
                          What's stock timing at wot like 35*?

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                            #43
                            I found detonation occurs somewhere around 20-23 degrees on my 9.5:1 CR under boost when IATs approach 100 F.

                            It was safe up to 25 degrees when IATs were below 50 or 60 F.

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                              #44
                              Originally posted by downforce22 View Post
                              I found detonation occurs somewhere around 20-23 degrees on my 9.5:1 CR under boost when IATs approach 100 F.

                              It was safe up to 25 degrees when IATs were below 50 or 60 F.
                              What about with E85? That should play a huge role vs pump gas
                              - AXIS POWERS - 2JZ E30 Build
                              Interested in drifting in the ArkLaTex? Join us!
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                                #45
                                Originally posted by lowr3v'in View Post
                                what's stock timing at wot like 35*?
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                                john@m20guru.com
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                                Transaction feedback: Here, here and here. Thanks :D

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