New member planning mods to 90 STS
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HT4100 4.1, 4.5, 4.9 Discussion, New member planning mods to 90 STS in Cadillac Engine Technical Discussion; Hi everybody, my name is Steve and I just signed up on here. I have spent the last few visits ...
  1. #1
    SS427 is offline Cadillac Owners Member
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    New member planning mods to 90 STS

    Hi everybody, my name is Steve and I just signed up on here. I have spent the last few visits reading old threads and I have learned a lot so far and hope I can eventually help other people out as well.

    I have been restoring late 60s 427 Chevy Impalas with my father to factory specs since I was about 7, and I bought this 90 STS in the summer of 05 as my first car. The time has come to start doing some mods to it to see what I can get out of it. I plan to do some intake stuff to the 4.5 along with some slight ignition adjustments, but for now I am just getting ready to install a flowmaster 80 series crossflow on my cad.

    My question is does anybody with a 90-91 STS or ETC know the measurements of the two tailpipes? I am planning to use some adapters to reduce the pipe size down so the tailpipes can be adapted into the muffler which has 2.5" inner diameter outlets. I think they are two inch outer diameter, but I can't find my caliper and need the car to get to work and school. For this reason, I can't rip everything apart yet, and once I do, I want to have everything I need right there so I can do it in a day or so. Once again I look forward to learning a lot from everybody and I am glad there are places like this for Caddy fans to gather.

    Please see the cardomain I just set up.
    http://www.cardomain.com/id/SS_427

    Steve
    Attached Images

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    awadecki is offline Cadillac Owners Enthusiast
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    Re: New member planning mods to 90 STS

    Don't know the answer, but just call an auto parts store and they can tell you what size the pipes are. Good luck with your mods. Are you trying to swap your intake with one from an Allante? That might be a good place to start.

  4. #3
    SS427 is offline Cadillac Owners Member
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    Re: New member planning mods to 90 STS

    Hi,
    Yes, I thought it would be a cool swap to try. Do you know if it is possible though? It is the same size engine, but is the intake manifold and fuel rail setup the only difference, or are there other things too like valvetrain and computer settings? I was able to get the correct adapters, which were 2.5 OD to 2 ID btw, and the exhaust is all done and sounds very nice. Not too obnoxious at all, just a nice deep rumble.
    Steve

  5. #4
    chazglenn3's Avatar
    chazglenn3 is offline Cadillac Owners Connoisseur
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    Re: New member planning mods to 90 STS

    Nice car, Steve! Mine is almost it's twin except it is a '91 without the rear console and has the 4.9L.

  6. #5
    illumina's Avatar
    illumina is offline Cadillac Owners Connoisseur
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    Re: New member planning mods to 90 STS

    Steve, I like what you have in mind, but because of the emission controls that are still abundant on the 4.5 liter, you're going to have some serious issues making what you need as far as engine add-ons are concerned.

    As for the Allante intake swap, you're best off using one from a 4.1 liter allante because you still need to run EGR to make everything agree with everything (ECM related crap)...Unless you know something about bypassing the EGR tables in the ECM; the 4.5 liter Allante didn't use EGR and using an Allante ECM is pretty much out of the question. That said, you will need to modify the fuel lines to mate to the Allante fuel rail, which you will need.

    As for other mods, a cool air intake setup is a tad harder for the 4.5 liter because of the exhaust re-breather (?) in the intake air box. Unlike as stated above, I'm not real sure if bypassing that will have an adverse effect on emissions/drivability. I am actually working on an air intake for my '87 Seville; the one on my '91 Seville worked out great! I'll let you know so as long as I remember to post it

  7. #6
    SS427 is offline Cadillac Owners Member
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    Re: New member planning mods to 90 STS

    Ohhh so the 4.9 doesn't have an A.I.R. pump?? I had no idea. It sounds like it would just make more sense to leave my 4.5 alone and just look for a 91 STS/ETC to experiment with! I would eventually like to engineer an N* into my 90, but that is somewhere way down the road and I will let everybody know when I start that project. Thanks for the post illumina, you sound know your stuff. Do you happen to know what I would have to do to lower my seville an inch or two? I think I have the rear figured out, but I dont know if I want to just cut the front coils.
    Steve

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    awadecki is offline Cadillac Owners Enthusiast
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    Re: New member planning mods to 90 STS

    SS427: The 4.9 has no AIR pump. You are correct.

    One easy modification you can do to get a few horses is to bump up your timing a few degrees. Just make sure to use premium and check for spark knock. Your car will definitely feel peppier, though.

  9. #8
    Chinman is offline Cadillac Owners Member
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    Re: New member planning mods to 90 STS

    I've got a '90 Seville. The first thing i did was remove the duct from the airbox to the radiator support. Very easy. Just take out the two plastic pins on the top and flex it down and it will come right off. Take a look at the end by the radiator support and you'll see why. The opening goes from a 2" by 6" rectangular opening down to a 1 7/8" round hole. VERY restictive. Once that is done, you can stick your hand inside the airbox and feel the filter. Put in a K&N filter or something similar. Yes it lets in more hot air than before, but hot air is better than no air.

  10. #9
    illumina's Avatar
    illumina is offline Cadillac Owners Connoisseur
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    Re: New member planning mods to 90 STS

    Quote Originally Posted by SS427 View Post
    Ohhh so the 4.9 doesn't have an A.I.R. pump?? I had no idea. It sounds like it would just make more sense to leave my 4.5 alone and just look for a 91 STS/ETC to experiment with! I would eventually like to engineer an N* into my 90, but that is somewhere way down the road and I will let everybody know when I start that project. Thanks for the post illumina, you sound know your stuff. Do you happen to know what I would have to do to lower my seville an inch or two? I think I have the rear figured out, but I dont know if I want to just cut the front coils.
    Steve
    I'm experimenting with actually raising and stiffening my rear-end an inch or so by shimming the outer edges of the transverse leaf-spring (Seville and Eldorado) on the rear control arms. I'll let all know how that works out; I would imagine that you could shim the center of the leaf-spring to lower the rear some. This should help eliminate or at least reduce rear-squat on the hard take-offs that I have in mind, but may cause more sway in the rear end when cornering...

    For the fronts, you can either cut the springs or perhaps find a way to bolt them down with one of those lowering kits you use on trucks. It's at least something to look in to.

  11. #10
    SS427 is offline Cadillac Owners Member
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    Re: New member planning mods to 90 STS

    That is a good idea for the fronts. On the rear, I bent the leveling sensor arm to trick the computer into pumping less air into the rear struts. It left the ride quality the same, and I can probably just bend it of I want it any lower or higher. I will look into the front this week.
    Steve

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