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Thread: '78 M30 Head Upgrade

  1. #1
    Join Date
    May 2009
    Location
    AK
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    21
    My Cars
    '79 Euro 635CSi 5spd

    '78 M30 Head Upgrade

    So I pulled the head from my '78 633CSi to find multiple cracks and thought about replacing it with a used 87-89 635csi complete head (valves, cam, ect.)

    My question is if replacing the head what extra parts should I think about adding to my shopping list if just swapping out heads. I know the distributor is different in the newer head but unsure of other needed changes.

    I plan to replace the factory exhaust header/reactor with a aftermarket header and removing the EGR system completely. And was thinking about also replacing the intake manifold with the 85 and up smother style. If also upgrading the intake manifold what extra parts should I consider upgrading.
    I realize some of the vacuum system from the 78 will then be changing just not sure the entire scope of the needed alterations.

    Any info would be helpful, just trying to work my way through things before I make a final decision.

    Thanks,
    MattMann

  2. #2
    Join Date
    Feb 2007
    Location
    Colorado
    Posts
    2,760
    My Cars
    E28s
    There a couple of thing you will encounter with this plan. The first is that the '87-89 head (B35) will lower the compression significantly. To retain your stock compression ratio you should look for a head from another 3.2 or 3.4 up to 1987 (through the end of production in E28s), and they should pretty much all be the same casting. If you get a head from a motronic car you will need to reuse your timing cover and the distributor drive from the front of the cam. Otherwise everything should bolt up and work just fine.

    Changing to the late style manifold will require quite a bit of work as well. For starters you won't be able to use your current throttle body, fuel rail or injectors. You will also need to modify your throttle linkage or convert to the cable style setup since you've got the rod style linkage right now. I think you will be able to get a TPS and injectors that are compatable with the L-Jet electronics, but I'd make 100% sure before you dive in!
    '88 528e /// '88 M5 /// '89 951 /// '98 E430 /// '02 M5

  3. #3
    Makr's Avatar
    Makr is offline Snark engineer PHD Moderator
    Join Date
    Jan 2004
    Location
    SL,UT
    Posts
    4,684
    My Cars
    '85 635
    I went the other way. Earlier head on later block.

    I used the same cam as I didnt want to pull that pain in the ass out.

    I machined a split nut to hold the rotor on. :rulaiz
    Any fool can make a rule, and any fool will mind it.
    Henry David Thoreau

    Ride fast, safety last.


  4. #4
    Join Date
    Jan 2007
    Location
    Norman
    Posts
    735
    My Cars
    '83 633CSI
    Does your head say M90 on the front?

  5. #5
    Join Date
    May 2009
    Location
    AK
    Posts
    21
    My Cars
    '79 Euro 635CSi 5spd
    Thanks for the info, some things in there I hadnt thought about yet.

    After a bit more research I decided to go with changing the 78 633csi to 84 633csi. Plans are to replace head, intake manifold, exhaust manifold+entire exhaust system, throttle body, air flow sensor, injectors, fuel rail, motronic control unit, ingition wires, distributor, throttle position switch, throttle cable setup and im probably forgetting something, all from '84 633csi system.

    Think it would work? Anything important im missing?

    Thanks again.
    MattMann

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