Convert 98 SLS motor into STS motor?
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Northstar Engines and System Technical Discussion Discussion, Convert 98 SLS motor into STS motor? in Cadillac Engine Technical Discussion; I have a 98 Seville SLS, and I am going to have to take it all apart to fix the ...
  1. #1
    bajarails is offline Cadillac Owners Member
    Automobile(s): 98 sls Northstar
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    Convert 98 SLS motor into STS motor?

    I have a 98 Seville SLS, and I am going to have to take it all apart to fix the head gaskets. I also have access to STS heads, which have less miles, and a STS ECU. Can I convert by changing heads (and therefore cams) and ECU?

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  3. #2
    chubbyranger is offline Cadillac Owners Connoisseur
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    Re: Convert 98 SLS motor into STS motor?

    IIRC the final drive ratio in the transmissions are different from SLS to STS so it would not buy you much to add the 25 HP. Given the complexity of these cars, trying that conversion could come back to bite you.

  4. #3
    zonie77 is offline Cadillac Owners Connoisseur
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    Re: Convert 98 SLS motor into STS motor?

    You would lose torque. If you change the differential gears and computer you are OK. If you only change the heads you will be sorry.

  5. #4
    bajarails is offline Cadillac Owners Member
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    Re: Convert 98 SLS motor into STS motor?

    OK, so I can put a STS transmission in also to get the right final gearing, it will work. I have access to the transmission also.

  6. #5
    Submariner409's Avatar
    Submariner409 is online now If it won't run, slap in a big stereo
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    Re: Convert 98 SLS motor into STS motor?

    Not only the transmission PCM section but also several other vehicle control and security modules have the original VIN in memory. They will have to be programmed to work with a different PCM, or the substitute PCM will have to be reprogrammed to work with the original vehicle controls. It ain't all that easy........and OBD-II isn't as programmer (there aren't any) friendly as OBD-I or later CAN electronics.

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