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Turbo M10 engine build

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    Turbo M10 engine build

    Hello, I am currently working on a turbo m10 build for my e30. I plan on running a 2002 crankshaft (2.0L) with the 1.8 block and head and a single chain crank sprocket. I was hoping for some suggestions as far as pistons to use (I plan on running 135mm rods) and I was hoping to avoid buying any custom pistons due to the pricing of them. I was hoping to keep compression somewhat stock/slightly lower it in order to run boost efficiently. I am aware many people have done the crank swap, I was hoping to get some direction as far as the proper pistons to buy for the engine build. it is worth noting I do plan on running an MLS headgasket.

    #2
    the later m10 ran piano top pistons. the 02 in 2.0L had flat tops. don't think the flat tops work with the 1.8 head and the piano tops won't work with the 2.0 crank. check the part numbers on e21s for 1979 on the 2.0 and then 82 or 83 for the 1.8. the changes occurred in the e21 era. the later e21 m10 head and pistons were carried over to the e30.

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      #3
      Are you planning to use the E30 1.8i head? Late E30 M10 pistons are lower compression than the early ones (1984), which have a large circular dome. Keep in mind that the M10 had a few different combustion chambers, some more open than others. There should be pics out there somewhere, maybe the Metric Mechanic website?

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        #4
        1976 49 state legal 2002's came with flat top pistons and the E21 2.0 head (not to be confused with the 1.8i head that came on later E21's and E30 M10's). These were ~8.1:1 compression with the E21 head and *should* work with the 1.8i head.

        1.8 pistons will not work with the 2.0 crank because the rod length is the same between 1.8's and 2.0's...you need the relocated wrist pin placement to avoid catastrophe. You could also source a 2.0 E21 head and piston set from a '77-'79 USA E21 320i as a set but the compression may be too high for your needs.

        Another thought if you have access to a lathe...you could try shaving the dome off of another 2.0 style piston to more of a flat top style. Would probably take quite a bit of trial/error and measuring or hit the easy button and pick these up:

        Price: $750 Location: Massachusetts Description: These pistons were intended for an M10 turbo build that was repurposed to a naturally aspirated build. The pistons & rings were installed but have never been fired. Technical Data: JE 8.5:1 Pistons w/ total seal gapless rings. Includes wrist pi...




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          #5
          Correct: "1.8 pistons will not work with the 2.0 crank"

          I'm guessing it may relate to combustion chamber and valve size but I'm not exactly.sure. If anyone can elaborate on the exact differences, that information would be greatly appreciate and may be helpful to others as well. Thanks for your assistance.

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            #6
            With stock 135mm rods and a 2l crank, if you're using the 1.8i head, you can use the 2L E21 flattops for something around an 8:1 compression ratio.
            You'd need to measure your head volumes after valve work to get an accurate static number...

            The spec for the E21 (with E21 head, not 1.8i) flattop's a mm or so down in the bore, and that will get you an almost period- correct compression ratio.
            That said, the 2002- spec piston with the open 1.8i head's going to be pretty low, too.
            I've never seen a 1.8i piston without a small pop- up dome...

            All that and the above said, finding pistons these days is getting a bit tough, and you may find that a forged custom slug's not going
            to cost much more than trying to find stock pistons, depending on what Mahle's pooping out of China these days...

            ...and with a modern fuel injection system, you might find that the 1.8i head can take a bit more modern (higher) compression ratio,
            depending on how boosty you want to get.

            t
            would pay the extra few hundred and run forged.
            now, sometimes I just mess with people. It's more entertaining that way. george graves

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