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325e M20B27 -> M20B25

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    325e M20B27 -> M20B25

    I can get a full M20B25 swap for somewhere under $1,000 ($750 with everything needed for the swap). I originally wanted to an M50 swap, but I don't really want to sink that much money in right now. Is this a reasonable price? How difficult will the swap be?

    I searched on this forum and there was good info (mainly regarding wiring issues) but nothing definitive. Is there a guide/write up on it?

    Thanks
    Last edited by Andy348; 10-04-2010, 04:51 PM.

    #2
    What year is your car? If it's an early model, there's a little more work as far as wiring is concerned, late models aren't too bad.

    Is there a reason you don;t keep the 2.7 block and put in the i head and ECU?
    john@m20guru.com
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    Transaction feedback: Here, here and here. Thanks :D

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      #3
      Originally posted by ForcedFirebird View Post
      What year is your car? If it's an early model, there's a little more work as far as wiring is concerned, late models aren't too bad.

      Is there a reason you don;t keep the 2.7 block and put in the i head and ECU?
      1986 325.

      It's already got 242,000kms and an undiagnosed rough idle and hesitation.

      How much would the I head and ECU cost? Would it simply make my engine pretty much a B25?

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        #4
        It's not quite the same, little less compression. If you have that much mileage, I see where you are going with it, though.
        john@m20guru.com
        Links:
        Transaction feedback: Here, here and here. Thanks :D

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          #5
          242000 kilo is only like 150k miles. I'd say convert the car to an 'i' and put an 'i' cylinder head on it. If you mill it even a little bit, like .010" it'll raise the compression and make more total area under the power curve than a B25.

          More than likely the rough idle is due to the l-jetronic fuel/idle management in the early cars. It is crap, and by converting the car to using Motronic 1.3, plus new vacuum hoses etc while you put the new head on, you should have a happy running m20.
          sigpic

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            #6
            Read this thread

            http://www.r3vlimited.com/board/showthread.php?t=100939
            sigpic

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              #7
              Oh, didn't catch the km lol. 150k miles isn't a lot for an m20 bottom end. Mine has 90k miles and I JUST did the swap not long ago. It is an awesome upgrade!

              Don;t be so concerned about the compression thing, the 2.5 has 8.5:1 and the 885 top end on a 2.7 block is 8.3:1, .2:1 is not a lot of compression to lose.
              john@m20guru.com
              Links:
              Transaction feedback: Here, here and here. Thanks :D

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                #8
                I can attest to the post above. I went for a ride in John's car and its Much faster than the standard 2.5 even with the .2 to 1 loss. Plus the combo just screams for boost!
                Build your own dreams, or someone else will hire you to build theirs!

                Your signature picture has been removed since it contained the Photobucket "upgrade your account" image.

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                  #9
                  Originally posted by rcfanatic View Post
                  242000 kilo is only like 150k miles. I'd say convert the car to an 'i' and put an 'i' cylinder head on it. If you mill it even a little bit, like .010" it'll raise the compression and make more total area under the power curve than a B25.

                  More than likely the rough idle is due to the l-jetronic fuel/idle management in the early cars. It is crap, and by converting the car to using Motronic 1.3, plus new vacuum hoses etc while you put the new head on, you should have a happy running m20.
                  I've read that you pretty much need every part from the M20B25 except the bottom end.. is this true? Or can I just use the "i" head?

                  What stress will this be putting on the bottom end?

                  And I'll try that fix for the idle as soon as the car gets back from the shop, unless they've found it to be something else.

                  Originally posted by rcfanatic View Post
                  Well, that answers my above questions.

                  Looks like I'll be scrap yard hunting. Will there be a large difference between me getting the necessary parts and the optional parts? Do I need to do any work on the pistons or is this strictly bolt on the I parts, change the electronics and go?

                  Originally posted by ForcedFirebird View Post
                  Oh, didn't catch the km lol. 150k miles isn't a lot for an m20 bottom end. Mine has 90k miles and I JUST did the swap not long ago. It is an awesome upgrade!

                  Don;t be so concerned about the compression thing, the 2.5 has 8.5:1 and the 885 top end on a 2.7 block is 8.3:1, .2:1 is not a lot of compression to lose.
                  Okay, thanks.

                  I'm really starting to consider doing this... is it a lot easier than an M20/M50 swap? Less costly I'm guessing...

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                    #10
                    Originally posted by Vedubin01 View Post
                    I can attest to the post above. I went for a ride in John's car and its Much faster than the standard 2.5 even with the .2 to 1 loss. Plus the combo just screams for boost!
                    Currently reading the two books posted in the Turbo tech section as a guide. This really appeals to me if down the road I can make it a monster turbo set up...

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                      #11
                      I'm still finishing up my b27 to b25 swap.

                      Whether you do just the head swap or the whole b25 motor, you'll have to do some wiring harness and top end stuff (intake, injectors, tb, afm) anyway. As a result, it's only a tiny bit more work to do the whole motor...that tiny bit being the short block though, which is kinda heavy. I was gonna do just the head, but by the time I got all the parts together (my last parts gathering adventure actually) I found an entire motor for a good price and just went with that instead.

                      While you have the b25 out, it's also a great time to swap in new parts that are cheap but really difficult to get at normally. Things like bearings, piston rings (and de-glazing cylinders), clutch, rear main seal, oil pan gasket etc.
                      sigpic

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                        #12
                        Watch the video link in my sig and tell me how nice the 2.7i is. That was with the 2.93 differential that came in the car, currently running a 4.11 and new exhaust, the car is has a little more hesitation now, but that's because I am running even leaner than before (I was at 15:1 afr's on the dyno o.0), so if you are not going to do any tuning, going to the 3.5bar fuel pressure regulator would be a good idea in my opinion (you can find them in Porsche's and are a direct fit.

                        When using a JY head, look for a clean one, maybe one that appears to be welded near the rocker shafts, that means they broke a timing belt since the car was new and the head was rebuilt.

                        Another tip is replace the little seals at the ends of the rocker shafts, they tend to leak once messed with and a lot of shops will re-use them, this will result in a surging idle - and don't forget the o-rings at the ends of the oil return tube between the block and bottom of the manifold (also will cause surging idle). These few little things that are easy to replace while you have it apart are not only cheap insurance, but also tough to replace once everything is together.

                        Make sure you get the entire brake booster hose from the donor car, crank position sensor, oil pressure sensor sender and low oil level switch since these are different on late model cars (as well as injectors, intake mani, throttle body etc), in fact you should keep this thread going as you get the parts so we can help you in case you miss anything. I did the swap after reading quickly through strictlyeta.net and ended up making a couple more trips o the junk yard.
                        john@m20guru.com
                        Links:
                        Transaction feedback: Here, here and here. Thanks :D

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                          #13
                          If you can find one, the early 1987 325i harness (with a C104 connector by the ECU plug) doesn't require any modification to work on a 1986 ETA chassis. It's the only one that is plug and play, any other harness will have to be modified. This is assuming you have a 1986 ETA, with a round C101 engine harness plug.

                          The early "I" engine harness has a small square C104 connector that goes in the glove box. The later "I" harness doesn't have that connector, as everything is routed through the main C101. You can still use a later harness, but you'll have to route a few wires from the C101 to your C104. That probably sounds confusing.... More info here
                          | Jimmy | 1999 M3 | 1986 325 ES |

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                            #14
                            Actually, I used the later i harness since it has the easy-release injector plug. I only had to jump 2 wires in the glovebox to the harness coming off the ECU to make the tach and econoguage work, everything else was under the hood. Either way, you will have to open the hole in the firewall a bit to get the ECU plug through it.

                            Also I just remembered the oil pressure sending unit will work with the new ECU/harness, just clip the plug off the end and put a female spade connector on it, but the dynamic oil level sensor was swapped out. Also the starter wires were clipped and added 2 female spade connectors instead of the eyelets for the small starter bolt connectors.

                            Try to get the 173 ECU if you can, I have both and use the 153 as my test bed for the emulator tuning now.
                            john@m20guru.com
                            Links:
                            Transaction feedback: Here, here and here. Thanks :D

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                              #15
                              Originally posted by Andy348 View Post
                              I'm really starting to consider doing this... is it a lot easier than an M20/M50 swap? Less costly I'm guessing...
                              I've never done an entire swap, but it depends on which tools you have. If you have an engine hoist and lift, then I would just do an M50 swap and be done with it. A B27 bottom with a B25 head that is milled makes more power than a B25. So a B25 swap is pointless *unless* you are trying to run Spec E30 which has guidelines requiring a stock B25 motor.

                              As far as cheaper, it can completely vary depending on how good of deals you get on parts. It is definitely cheaper to do the head swap than an entire M50 swap though.

                              When you're hunting for a head I suggest you keep looking until you find one that has NO signs of damage. Pay special attention to the wear on the cam and rocker arms. Inspect the valves and their margins as well as the rocker shafts for signs of abuse. Have a look at the bottom side of the head to see what kind of finish it has. If it is rough then it may have already been milled previously.

                              In fact, my best advice is to just spend the $600 and buy a remanufactured 885 head. I could have bought TWO remanufactured heads with the amount of money I spent rebuilding a used head I purchased. It will save you time, money, and peace of mind.

                              Try to get the 1989 engine harness and the 173 DME. Here are the things I used in mine

                              1989 engine harness
                              complete i intake (afm, icv, manifold, throttle body, tps, injectors)
                              i dme (173 is ideal)
                              i fuel pressure regular
                              i speed sensor (reads from the front crank pulley)
                              i o2 sensor (there are two, get the right one for the harness you find)
                              coolant temp sensors (blue and brown)
                              sigpic

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