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Thread: My EVO 4 Build thread.... it will be slow....

  1. #11

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    *drools* .
    - 1996 XI Honda Integra J32, ITR Clone -
    - 2001 GDB STI WRB, Lachute Power Plant-
    - 1992 Honda Civic SI K20a2 -
    - 2001 Honda S2000 -

  2. #12

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    A few things I found out about the rear diff in the evo 4's:

    The rear diff has an early version of ayc which doesn't work very well and can fail under higher hp applications. For this reason I'm going to convert to a mechanical diff.

    I then researched different options for that, there are a few. Cusco and Kaaz make mechanical duffs that will go in the stock case. However this doesn't solve the problem of the ayc case being weak. Under higher hp apps. The case will crack (ayc case)

    The next option is using the rs diff from an evo 4. I have to say, good luck finding one. They are rare. I did manage to find one in the uk but the going price for these set ups is 1600 pounds shipped to canada.... So $2800.

    A cheaper way of addressing this is buying an evo 8/9 non ayc diff. Lucky for us all usa/canada market evo 8/9's came with the rs diff stock. Mr111746 is the part number stamped on the case.

    2 issues with this, one the ratio is slightly different, two the axels are slightly longer.

    I have spoken to a couple shops about the difference in ratio.... It is very small. So small that none of the shops think it will cause a failure or put any undue stress on the drive train.

    The axels being 20mm longer is not a problem if you keep stock ride height. If you lower the car it will become a problem since the ends if the axels will bottom out. To correct this you can use '98 (8th gen) vr4 axels. They are the same length as the evo 4 rs axels.

  3. #13

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    Looking good so far! Slowly bud surely building this thing up
    1998 Mitsubishi Lancer Evolution V (Silver) - Sold
    1998 Mitsubishi Lancer Evolution V (White)
    2009 Triumph Street Triple R (Matte Orange)
    2004 Subaru Forester 2.5X

  4. #14

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    Would an Evo 6 RS diff work better?

  5. #15

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    I thought you could just change the diff with an Evo 7 one?
    CA_FTW Says ^^^^^^^^^^

  6. #16

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    Nice Evo IV! The RCII's suit it well.

  7. #17

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    Would an Evo 6 RS diff work better?
    All the rs diffs are basically the same from 5-9. The issue is the axels are different lengths. The 5 and 6 have a wider track then the 4. So a 6 rs diff and an 8 rs diff are really negligible. The issue is making them fit the 4 due to axel length.

    I thought you could just change the diff with an Evo 7 one?
    From my research the rs diff from 4-9 will fit, the issue has always been axel length.

  8. #18

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    I have continued to research rear diff options for my evo 4 with the goal of getting rid of the ayc.

    Through my reading I found out that there are big similarities between the evo 4 rs rear diff and the cm5a 1.8 turbo gsr.

    The cm5a chassis that is similar to the mirage has the following rear diff similarities:

    - the case of the rear diff is the same as the evo 4 rs. However the diff itself is an open diff.
    - the axels are the same length as the evo 4 rs but not as thick.
    - the hangers, moustache bar are the same.

    So what this means is that you can get a diff set up with an rs case for cheap. Then the next thing you would do is get an rs diff insert installed ( the guts) to make it a true locking 1.5 way. The insert would need to be from a jdm or ukdm rs evo as the friction plates are configured in a more aggressive way. The ones from the USA that are all over ebay are not set up as a true 1.5 way diff. The frictions can be replaced and re- arranged to solve this but that's another cost.

    Then what's left is upgrading the shafts but which could be done by a place that does custom axels but at least you'd have a template for them to work from being the cm5a ones.

  9. #19

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    I'll keep this updated as I ordered cm5a set up for the case and axels, and an evo 9 ukdm rs diff shipped for $1000 less than a real evo 4rs set up. The only drawback is the axels but I'm betting I can get custom ones made for less that will support far more than the 4 rs ones. It's also a bonus getting the newest rs diff out of the 9.

  10. #20

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    Nice score, where did you order the parts from?

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