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m20 stroker confusion....

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    #16
    Originally posted by Sean
    Pistons are different.
    ok, but what you were speaking of was removing a super-eta head from a super-eta bottom end, and then putting on an i head.

    so the pistons aren't what's changing.

    and the heads are the same casting.

    so how is the CR not still 8.5:1?
    past:
    1989 325is (learner shitbox)
    1986 325e (turbo dorito)
    1991 318ic (5-lug ITB)
    1985 323i baur
    current:
    1995 M3 (suspension, 17x9/255-40, borla)

    Comment


      #17
      Originally posted by dk
      Originally posted by Sean
      Pistons are different.
      ok, but what you were speaking of was removing a super-eta head from a super-eta bottom end, and then putting on an i head.

      so the pistons aren't what's changing.

      and the heads are the same casting.

      so how is the CR not still 8.5:1?
      Ohh, got confused there. I thought he meant something else lol

      And...wow, you're right! :shock:
      - Sean Hayes

      Comment


        #18
        so, the only way to get a little higher compression is to use "i" rods....


        u take eta (88 super), throw "i" rods in it, and I head... then u have a 2.7, with "ok" compression..... b/c the thing that gives it the 8:1:1 compression is the eta rods .. (right)
        </img>
        Schnitzel Not Rice....

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          #19
          Originally posted by Switch
          so, the only way to get a little higher compression is to use "i" rods....

          u take eta (88 super), throw "i" rods in it, and I head... then u have a 2.7, with "ok" compression..... b/c the thing that gives it the 8:1:1 compression is the eta rods .. (right)
          NO.

          eta crank + i rods + any stock pistons = pistons banging into cylinder head.

          think about it. you're adding 3mm of height at TDC, and there really is not that much room.

          again, if you have a super-eta bottom end already, you don't need to do anything to it to fit an i head (or as stated, you can just do the valvetrain swap instead; but that involves pulling the head anyway, which pretty much makes it a wash as to which is easier, IMO).

          if you want to use i pistons with an eta crank, you need custom rods that are 3mm shorter than the i rods are. there is simply no way around that.

          the ONLY way to do a high-compression stroker with factory parts is with an eta bottom end and a 731-casting head. and even then you need to big-valve the head up to "i spec" if you want it to be a worthwhile effort (again, IMO).

          sorry if i sound overly emphatic, i just don't want someone to waste time putting together an engine that will self-destruct on the first crank.
          past:
          1989 325is (learner shitbox)
          1986 325e (turbo dorito)
          1991 318ic (5-lug ITB)
          1985 323i baur
          current:
          1995 M3 (suspension, 17x9/255-40, borla)

          Comment


            #20
            thanks, sry i thought i heard somewhere u can use super eta pistons with i head and it will not conflict.. oh well..


            so.. how much better is a 2.7 w/ 8:1 compression (super eta plus i head.. done) , then a stock "i" lol
            </img>
            Schnitzel Not Rice....

            Comment


              #21
              Originally posted by Switch
              thanks, sry i thought i heard somewhere u can use super eta pistons with i head and it will not conflict.. oh well..
              you can. but you have to use the entire super-eta bottom end in factory config, nothing changed.

              so.. how much better is a 2.7 w/ 8:1 compression (super eta plus i head.. done) , then a stock "i" lol
              go back and read the thread again. super eta plus i head is exactly the same compression ratio as a complete super eta motor- 8.5:1. the only thing that changes in that scenario is the valvetrain.

              i'm thinking the lower-compression motor Jordan was referring to is what you get when you slap an i head on a regular eta bottom end.

              and yes:
              2692cc @ 8.5:1
              will make slightly more power than
              2494cc @ 8.8:1
              with more area under the torque curve.

              which is not to say there aren't better alternatives out there- but if what you want to do is bolt together a bunch of parts you can easily find in junkyards, it's about the best you're going to do.
              past:
              1989 325is (learner shitbox)
              1986 325e (turbo dorito)
              1991 318ic (5-lug ITB)
              1985 323i baur
              current:
              1995 M3 (suspension, 17x9/255-40, borla)

              Comment


                #22
                your right, sry, should have just re read thread, it was like 5:15 when i posted (yawn) thanks alot for the info i appreciate it.
                </img>
                Schnitzel Not Rice....

                Comment


                  #23
                  If someone were putting an I top end on a Super Eta bottom end, they could deck the block a little to raise compression, couldn't they?

                  Or, would custom pistons just be the way to go?
                  - Sean Hayes

                  Comment


                    #24
                    You guys are thinking about this whole thing wrong with the super eta. The super eta head is the same exact casting as an i, so what's the point in changing heads, just change the springs and cam and you're done. Since you'll have the head off, shave it to spec to increase compression.
                    Driving is the only way to go faster....

                    Comment


                      #25
                      If someone were putting an I top end on a Super Eta bottom end, they could deck the block a little to raise compression, couldn't they?
                      And you can do this as well as shave the head to further increase compression. Just be careful how far you go or the timing will be off and you'll run the risk of valve slap very quickly.
                      Driving is the only way to go faster....

                      Comment


                        #26
                        I made a typo guys, chill.

                        8.5:1 is still weak.

                        metric mechanics sell a offset dowel pin for the cam gear to correct for decking the head and block. Either way I don't recommmend doing this to increase compression.


                        E30 ABS Pump Refurbishment Service
                        https://mtechniqueauto.com/

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                          #27
                          Originally posted by Jordan
                          8.5:1 is still weak.
                          *nod* the only config i see really taking good advantage of a super-eta bottom end is a turbo setup... for that, more displacement + slightly less compression is a good thing.

                          otherwise, either custom pistons, custom rods, or some cross-pond parts hunting is on the menu.
                          past:
                          1989 325is (learner shitbox)
                          1986 325e (turbo dorito)
                          1991 318ic (5-lug ITB)
                          1985 323i baur
                          current:
                          1995 M3 (suspension, 17x9/255-40, borla)

                          Comment


                            #28
                            i'm really just looking for a little more low end torque, since i figure thats the weak point of the 2.5.

                            would simply super eta, w/ i head (cam whatever) be the ticket to same power of 2.5 + a little more low end torque?
                            </img>
                            Schnitzel Not Rice....

                            Comment


                              #29
                              Its not that much, you gain about 15 ft/lbs at most. But like in the previous post, if you're going turbo, then just slapping the "i" head on the super eta bottom end is a decent candidate for a low compression engine.

                              Comment


                                #30
                                yeh, if only i had 2 to 3 grand to toss into it... i'd have a nice shiny blow off and everything *dreaming* *VROOOOM... PSSSHH*
                                yes.. that would be nice... i guess the best thing i can do right now is chip it, intake and exhaust,,,
                                </img>
                                Schnitzel Not Rice....

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