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What to do with 300k miles?

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    #1

    What to do with 300k miles?

    Recently picked up a 88' 325 with 306,000 miles. I want to build an m20, I have been pricing out a 2.7 build including new main and rod bearings, double valve springs, new valve seals, a pretty aggressive cam (possibly cat cams 285/285), new rockers, I intake manifold, throttle body, fuel rail, ecu, top and bottom end gasket kit, timing belt and tensioner, port and polish on the head and intake manifold.

    However the only weak point I can see with this set up is reusing a block/rotating assembly with 306,000 miles, I figured I would do a compression test before I pull everything apart and see what kind of numbers I get.

    What numbers should I expect to see if I do a compression test?

    Also would it be worth it to source a less mileage 'e' block, get some custom pistons, 524td crank, etc?
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    #2
    I just tested the compression on my m20b25 that has 250k miles on it with a broken odo and the highest number I got was 131psi and the lowest was 119psi I have been told that it is acceptable as long as the lowest number is no less than 85 percent of the highest number for example my highest was 131psi so my acceptable range is 131-111

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      #3
      Hey thanks for the good info, helps a lot, I will post the results when I do the test.

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        #4
        A 300k block almost certainly will beed a rebore and new pistons. The crank probably only needs polishing, but measurement of the crank journals will tell.
        The car makes it possible, but the driver makes it happen.
        Jim Levie, Huntsville, AL

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          #5
          Originally posted by jlevie View Post
          A 300k block almost certainly will beed a rebore and new pistons. The crank probably only needs polishing, but measurement of the crank journals will tell.
          That is what I have been worried about, however in this case I would probably bore to 86mm, custom pistons, low mileage 524td crank, then hopefully find a cheap low mileage 'i' head, cam it, and port and polish. Just not trying to pour thousands into an m20 lol.

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            #6
            24v swap it for more power, less money, less down time of the car
            "God created turbo lag to give V8's a chance" Taylor D.

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              #7
              look into the castrol 1 million mile test on youtube. They drove an e30 1,000,000 miles and it still had the factory cross hatching. Of course that did not take into account idling, cold starts, overheats, bad maintenance etc but it is a testament to the strength of the m20.
              318iS Track Rat :nice: www.drive4corners.com
              '86 325iX 3.1 Stroker Turbo '86 S38B36 325

              No one makes this car anymore. The government won't allow them, normal people won't buy them. So it's up to us: the freaks, the weirdos, the informed. To buy them, to appreciate them, and most importantly, to drive them.

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                #8
                thought that was the mobil1 E30
                "God created turbo lag to give V8's a chance" Taylor D.

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                  #9
                  Originally posted by 1987_325is View Post
                  That is what I have been worried about, however in this case I would probably bore to 86mm, custom pistons, low mileage 524td crank, then hopefully find a cheap low mileage 'i' head, cam it, and port and polish. Just not trying to pour thousands into an m20 lol.
                  Rebore, crank, pistons, & rods will have you at, or above, a thousand. The head is where all the magic happens and a full rebuild of a used head (and a cam) is another thou. A lower mileage M20B25 engine is going to produce almost as much power as what you contemplate and be a whole lot less expensive. An M50 swap will be about equal and cost no more.
                  The car makes it possible, but the driver makes it happen.
                  Jim Levie, Huntsville, AL

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                    #10
                    Originally posted by downforce22 View Post
                    look into the castrol 1 million mile test on youtube. They drove an e30 1,000,000 miles and it still had the factory cross hatching. Of course that did not take into account idling, cold starts, overheats, bad maintenance etc but it is a testament to the strength of the m20.
                    That's an incredible video, I don't know how i haven't seen it before. Thanks for the heads up. Definitely makes me a little less worried.

                    Originally posted by 5KWattson View Post
                    24v swap it for more power, less money, less down time of the car
                    I have 3 cars at the moment so I am not worried about down time to much lol, I also have enough parts laying around that I might be able to build about a 190 hp 2.7 spending under 1000. And I love building motors so would rather go this route.

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                      #11
                      Originally posted by jlevie View Post
                      Rebore, crank, pistons, & rods will have you at, or above, a thousand. The head is where all the magic happens and a full rebuild of a used head (and a cam) is another thou. A lower mileage M20B25 engine is going to produce almost as much power as what you contemplate and be a whole lot less expensive. An M50 swap will be about equal and cost no more.
                      Once I pull the motor apart I will know for sure where I am at. If the block is shot then I still have another eta block in decent shape that I would use the crank and rods out of, new main and rod bearings (300ish?), reuse the 88' seta pistons with new rings(idk how much), then I would plan on sourcing a low mileage 'i' head (400 max), add timing belt kit, gasket kit seals and all (300 max) and I'm looking at a grand, I can probably source parts for slightly cheaper. I haven't gathered exact values yet.

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                        #12
                        Anyone happen to know the best place to get quality oem engine parts? BMAparts seems like they have the best prices, just wondering if there is anywhere better. Thanks.

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                          #13
                          Originally posted by 1987_325is View Post
                          Anyone happen to know the best place to get quality oem engine parts? BMAparts seems like they have the best prices, just wondering if there is anywhere better. Thanks.
                          I have found no better than www.blunttech.com especially when it comes to prices.

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