The best engine to put in my Eldo Cadillac?
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HT4100 4.1, 4.5, 4.9 Discussion, The best engine to put in my Eldo Cadillac? in Cadillac Engine Technical Discussion; ...
  1. #1
    KINGUYOM is offline Cadillac Owners Member
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    The best engine to put in my Eldo Cadillac?

    Hello all fans of Cadillac!

    I have a big problem with my 1985 Cadillac Eldorado convertible, V8 engine 4100 ht is dying so I have to find a way to change it soon

    Browsing the web, I saw a lot of guys who have so changed that infamous original engine with a V8 5.7 liter, 350 ... it with a carburetor.

    I found several used engines on the web:


    • Option 01:
    A 5.7-liter v8 efi
    who come from a 1976 Cadillac Seville

    • Option 02:
    A 5.7-liter V8 carburetor
    who come from a Chevrolet Monte Carlo Landau Coupe

    • Option 03:
    A 5.7-liter V8 nine seen on the Summit website
    This GM performance V8 350 195 HP Engine C.I.D base


    Could you help me and tell me if these engines are mounted in my 85 Cadillac?
    especially if they can adapt to my transmission
    and my gearbox THM 325-4L?

    thank you in advance for your valuable advice

    friendly
    William

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  3. #2
    83CADMAN's Avatar
    83CADMAN is offline Cadillac Owners Fanatic
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    Re: The best engine to put in my Eldo Cadillac?

    A GM 350…sound good to me. I have an 83 Eldo with the HT4100 and have often though about engine upgrade.
    Cadillac offered a diesel, which by the way is an Olds engine based on the GM 350. I don’t know if they used a different transmission with the diesel option or not. If not then one would think that any 350 SB could match up to your stock bell housing. It’s all the computer stuff…

  4. #3
    aeronca36606 is offline Cadillac Owners Enthusiast
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    Re: The best engine to put in my Eldo Cadillac?

    Chevy 350 won't bolt up tp the transmission. The 1985 Eldorado used the old Buick Pontiac Oldsmobile bell housing. Chevrolet is different. With the space constraints with the THM325 transmission, I don't think a bell housing adapter would be an option. If you are going to use anything except the original HT4100 or 5.7L Diesel, Then your best bet would be either an Olds V8 or a Cadillac 368 or any engine in the 368 family. You could also use the Buick V6 as these where sometimes found in the Buick Riviera and Eldorado. (Usually in the 252ci version). Parts for the V6 conversion may be a bit hard to find though as this was a rare option. (I believe the V6 was available with a turbo also)

    Take it from someone that has done a few engine swaps in vehicles not originally fitted with the engine being swapped in. Conversions are always a headache unless you have a complete parts car with the configuration you are shooting for. It is almost never the big things that hang you up. It is the small things that cause all of the trouble. Like cables mounts brackets fuel systems starters etc that cause most of the work and expense.

    Unless you are looking for something the original engine can not provide (Performance?) then your best bet is to replace or rebuild the original power plant. The 4100 while not a power house by any stretch of the imagination, Is capable of propelling the car at reasonable speeds with reasonable performance while delivering excellent fuel economy. Fuel economy will only become more important as time goes on.

    There is also the possibility that your non emission compliant conversion will be banned from the road by an un-caring Department Of Motor Vehicles. Some states are very hard on conversions and most will become so in the next 10 years.

    Good luck with your project.

  5. #4
    vincentm's Avatar
    vincentm is online now Cadillac Owners Connoisseur
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    Re: The best engine to put in my Eldo Cadillac?

    Have you thought about getting the original engine rebuilt with possible updated gaskets, etc?

  6. #5
    dennis93coupe's Avatar
    dennis93coupe is offline Cadillac Owners Connoisseur
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    Re: The best engine to put in my Eldo Cadillac?

    After following ehall's 4.9 conversion in his DeVille, I'd be tempted to try that. It would save a complete engine tear down.

  7. #6
    KINGUYOM is offline Cadillac Owners Member
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    Re: The best engine to put in my Eldo Cadillac?

    Thank's a lot for your advices !

    aeronca36606, i think you right about the fact to have a donor car is the more simple way,
    a friend of mine have in his junkyard an CADILLAC ELDORADO 1981 With the 6.0 liter gasoline, may be i can buy it and transplate all the stuff to my eldo 85 ?

    ps : i live in europe, so don't care about state law
    also, excuse me for for my bad english...

    some picture of his car :

    a-81.jpgb-81.jpgc-81.jpg

  8. #7
    aeronca36606 is offline Cadillac Owners Enthusiast
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    Re: The best engine to put in my Eldo Cadillac?

    That particular car has the other infamous engine of the 80's. The V8-6-4. The engine itself is a strong design along the lines of the 472cu and 500ci engine. The problems are with the Valve switching technology. This was an early attempt at variable displacement. Unfortunately the control systems where not as developed as they should have been. This said I had a Fleetwood 75 Limousine with this engine and it ran flawlessly. The Variable Displacement system worked 100% as advertised. This is my only actual experience with this engine and it was good. However there have been many that have had a lot of problems with it. You can disconnect a sensor on the trans that will effectively disable the Variable Displacement control. This will let the engine run in the V8 mode all of the time. I tried this once on mine and it ran just as any normal engine would. The fuel economy did go down quite a bit but not excessively. These are a tough engine though and are known to take abuse without causing mechanical failure.
    Overall not a bad way to go in place of the HT4100.

    As much bad publicity as Cadillac has had with respect to there 1980's designs, There was a lot of innovation during those years.
    The HT4100 with all of its problems was in the for front of the move to electronic fuel control. It has some of the best on board diagnostics of the period. Even better than most of today's cars.
    The V8-6-4 was the first attempt to integrate a Variable Displacement engine into a mass market.
    The 5.7 Diesel was the first diesel experience most Americans had with Diesels. It sold in much bigger numbers than most people realize. It did have some problems with it's design (Most of which wouldn't have been there if accountants stayed out of the engineering of the engine) but was made reliable near the end of it's production run.
    During the early 80's there was a lot of change at Cadillac and they did a fairly decent job while bringing a lot of new technology to there cars.

    My favourite Cadillacs are the 67 to 70 Eldorado's. I have owned several of each and was sorry after each was sold. Your 85 is a sure to be classic and has some of the best lines of the era. It is also a great drivers car. I had a Brown 85 Eldorado and was very happy with it as a daily driver. (HT4100)

  9. #8
    KINGUYOM is offline Cadillac Owners Member
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    Re: The best engine to put in my Eldo Cadillac?

    Thank's again aeronca36606 for your knowledge !

    you say this engine is a V8-6-4 ?
    i don't know how to recognize this engine
    from a regular V8 6.liter :s

    how to recognize it visually?

    in the 1981 year, Cadillac make only this engine ? or they prodcut also regular V8 6.liter ?

    thank's

    friendly
    William

  10. #9
    aeronca36606 is offline Cadillac Owners Enthusiast
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    Re: The best engine to put in my Eldo Cadillac?

    Quickest give away is the tall and oddly shaped valve covers with the electrical connectors for the Valve Disconnect.

    I think the 6.0 was only in a V8 6 4 version. (Anyone correct me if i am wrong) I believe you can convert the engine to a conventional design. (Possible valve train or head swap)
    You may also be able to use a 400ci or 472ci as i believe these used the same basic block but further research would be necessary.

  11. #10
    KINGUYOM is offline Cadillac Owners Member
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    Re: The best engine to put in my Eldo Cadillac?

    thank's again aeronca36606

    you a really cadillac expert !

    i think in 1979 & 1980, they are not "regular" 6.liter only 5.7 liter....

    some pictures to be sure i have understand :
    v8-6-4_6liter.jpgv8 6liter.jpg

  12. #11
    watajob is offline Cadillac Owners Member
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    Re: The best engine to put in my Eldo Cadillac?

    That is a V8 6 4. And, to be clear, 79 had a fuel injected Olds 350 lifted from the Sevilles of that time, 80 an FI 368 Caddy, 81 had the 8 6 4 and 82 - 85 had the 4100. The 368 is the small end of the 368/425/472/500 family.
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  13. #12
    KINGUYOM is offline Cadillac Owners Member
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    Re: The best engine to put in my Eldo Cadillac?

    Quote Originally Posted by watajob View Post
    That is a V8 6 4. And, to be clear, 79 had a fuel injected Olds 350 lifted from the Sevilles of that time, 80 an FI 368 Caddy, 81 had the 8 6 4 and 82 - 85 had the 4100. The 368 is the small end of the 368/425/472/500 family.
    Thank's Watajob !
    you say " caddy 79 had a fuel injected Olds 350 lifted from the Sevilles of that time"

    that's mean it's not exactly the same engine ? the engine of a 76-79 Seville can be put in a 79 eldorado ?
    can you explain the differences ?

    thank's a lot
    William

  14. #13
    watajob is offline Cadillac Owners Member
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    Re: The best engine to put in my Eldo Cadillac?

    79 and 80 are totally different engines. As far as the swap, I don't know. 76 - 79 Sevilles were modified X bodies, (RWD). The new for 79 Eldo was part of the E body, (FWD), line. I'm sure there are people on here who could tell you. Or, try a search
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  15. #14
    KINGUYOM is offline Cadillac Owners Member
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    Re: The best engine to put in my Eldo Cadillac?

    Quote Originally Posted by watajob View Post
    79 and 80 are totally different engines. As far as the swap, I don't know. 76 - 79 Sevilles were modified X bodies, (RWD). The new for 79 Eldo was part of the E body, (FWD), line. I'm sure there are people on here who could tell you. Or, try a search
    I search on the web, and i see a guy who swap the 4100 ht (fwd) by a 350 ci ( rwd)
    and who said : the flywheel is differente
    Flywheel (it's specific to FWD if you're using a RWD configured engine)

    most of the time the 350ci from an Oldsmobile 98, but i don't know if the 76-79 sevilles have the same engine exactly ?

    your opinion ?

  16. #15
    watajob is offline Cadillac Owners Member
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    Re: The best engine to put in my Eldo Cadillac?

    I really couldn't give an opinion as I have no idea. I'm wondering if a post over in the Eldo/Seville forum might yield the answers you're looking for as there are some pretty knowledgeable folks over there. Sorry I couldn't be more help.

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