81 Coupe DeVille Engine swap
Cadillac
 

Cadillac Forums | Help Us Help You | Advertise | Cadillac Parts | Cadillac News | Cadillac Classifieds / (Old System)

Cadillac Technical Archive | Cadillac Dealers | Cadillac Reviews | Cadillac Dealer Reviews | Cadillac Vendors

CadillacForums.com is the premier Cadillac Forum on the internet. Registered Users do not see the above ads.
+ Reply to Thread
Page 1 of 4 1 2 3 4 LastLast
Results 1 to 15 of 55
RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, 81 Coupe DeVille Engine swap in Past Cadillac Vehicle Discussion; Hello all, I am new the forum and I spent some time searching for some information, didn't exactly find what ...
  1. #1
    asaddman is offline Cadillac Owners Member
    Automobile(s): 81 Coupe DeVille
    Join Date
    May 2011
    Posts
    26

    81 Coupe DeVille Engine swap

    Hello all,
    I am new the forum and I spent some time searching for some information, didn't exactly find what I was looking for.

    Here is the story, got this super clean 81 Coupe DeVille for dirt cheap, nothing wrong with the interior or exterior, but the engine was blown. Did the research with the VIN and all that to determine it is the 8-6-4 and personally don't really care for it regardless.

    So I found out that the 200r tranny that is in there will bolt up to a 350 Chevy engine. Other than that my main concern is the engine mounts and my components working right.

    Has anyone done this on the forum and had good luck with it, I saw someone had the V6 and were putting in a 305 and also saw someone saying that its better to go with the 454 due to the block is based off the same as whats in my car.

    I already have a nice 350 that I want to use, do you know what electrical issues I might have converting this over to a carb? Am I going to have problems trying to use the stock AC and cruise control options. What year/model can I use for motor mounts, is there any thing else that I am missing?

    Totally appreciate all the looks and responses a head of time.

  2. Remove Advertisements
    CadillacForums.com
    Advertisements
     

  3. #2
    sven914 is offline Cadillac Owners Connoisseur
    Join Date
    Dec 2008
    Posts
    4,164

    Re: 81 Coupe DeVille Engine swap

    You don't have a 200r and a 200 doesn't bolt to Chevrolet. You have a TH400, which mounts to Cadillac, Buick, Oldsmobile, or Pontiac V8's.

    The easiest thing to do would be to swap in a Cadillac 472 or 500; they are direct replacements for 368. The cheapest route would be to find an Oldsmobile 403 or 350 and put that in, but you might need to play around with the mounts.

  4. #3
    asaddman is offline Cadillac Owners Member
    Automobile(s): 81 Coupe DeVille
    Join Date
    May 2011
    Posts
    26

    Re: 81 Coupe DeVille Engine swap

    so is it not possible to put the 350 chevy in there? even if I replace the trans to match the motor, I realize that I will probably have to get a custom driveline.

  5. #4
    cadillac_al is offline Cadillac Owners Connoisseur
    Automobile(s): Cadillac 78 Seville, 78 Coupe de Ville, 92 Sedan de Ville
    Join Date
    Feb 2007
    Location
    Maine
    Age
    52
    Posts
    2,710

    Re: 81 Coupe DeVille Engine swap

    Yes you can asadman. GM basically uses 2 styles of motor mounts. I used to call them Chevy style and Olds style but I think I have seen both on Caddys so i never know which one has which style. When you pull out the Caddy engine, and if you see Chevy style mounts, it should be an easy bolt in. If it's the Olds style you can decide if you would rather change those frame pads or look for an Olds engine. Piece of cake bro.

  6. #5
    sven914 is offline Cadillac Owners Connoisseur
    Join Date
    Dec 2008
    Posts
    4,164

    Re: 81 Coupe DeVille Engine swap

    You don't need to replace the transmission either. You can get a BOP-Chevrolet adapter for the bell-housing. The disadvantage of this is keeping the non-economical 3-speed transmission (instead of upgrading to the Chevrolet's 4-speed). Also the adapter will create a weak spot in the drive-line, so you will be limited on power.

    I'm still questioning why you're hung up on the Chevrolet motor. If you are looking for a cheap alternate motor, then I recommend the Olds 350; there are lot of them around and there are a lot of performance upgrades for them.

  7. #6
    asaddman is offline Cadillac Owners Member
    Automobile(s): 81 Coupe DeVille
    Join Date
    May 2011
    Posts
    26

    Re: 81 Coupe DeVille Engine swap

    (I'm still questioning why you're hung up on the Chevrolet motor. If you are looking for a cheap alternate motor, then I recommend the Olds 350; there are lot of them around and there are a lot of performance upgrades for them.)

    Well I have a chevy 350 here at my house and I know it runs and don't have a lot of extra money for a lot of parts and such. But if need be it looks like whatever the best way to go about it will be what I do. I honestly haven't found many olds 350 here I am a craigslist junkie and I searched and have no good luck without dropping a good amount of money on a running engine.

    So what your saying though is that the olds 350 will bolt right into place, tranny and all? I was under the assumption the the 200r had a bellhousing pattern that will bolt to a chevy 350, I might be wrong, honestly I am a Ford guy and haven't done a lot of work on GM cars, if so they were chevy based engines not cadillac olds or pontiac. The engine mounts for the chevy 350 I don't think will be a problem, planning on going to the junk yard and seeing what I can find there that will work.

    Do you know if I am going to have problems (chevy or olds 350) with the fuel injection that is already in place in my car, will my fuel pressure be ok, will it even pump at all?

    Thanks

  8. #7
    sven914 is offline Cadillac Owners Connoisseur
    Join Date
    Dec 2008
    Posts
    4,164

    Re: 81 Coupe DeVille Engine swap

    Your car should have the TH 400 transmission; its a three speed (no overdrive). The 200r you keep referring to was not used with the 368; in '81 it was only offered with the Buick 6 cylinder and is a four speed. Both the 400 and 200 have the BOP (Buick, Olds, Pontiac) bell-housing, which doesn't fit Chevrolet; you can get a BOP-Chevy adapter to make it work.

    The '90-'92 Cadillac Brougham (RWD) used the Chevrolet 350 and was the same basic body as your de Ville. If you go with your 350, you should get a TH700 transmission (you can find them in most mid '80's to early '90's Chevrolet rear wheel drives) because it has an overdrive gear and will be more durable than the TH400 with the adapter. You can scavenge engine mounts and a drive shaft from a '90-'92 Brougham and this way you won't need to do too much customizing.

    The fuel pump for the 368 should be adequate enough to supply the demands of the 350. I do not think the computer in the '81 will be able to work with the newer motor, so if you are keeping it TBI, you might have to get a computer from a '90-'92 Brougham. Worse comes to worse, just get a carburettor and forget about the computer; nothing on the car, except the A/C compressor clutch, requires the computer.

  9. #8
    cadillac kevin's Avatar
    cadillac kevin is offline Cadillac Owners Master
    Automobile(s): chevy 350 powered 86 FWB, 00 safari h.t. 66 toro, 83 lesabre
    Join Date
    Dec 2010
    Location
    St. Louis, MO
    Posts
    5,604

    Re: 81 Coupe DeVille Engine swap

    the 368 (v8-6-4) is a cadillac motor and uses olds motor mounts.) you will need to change the mounts. it would be alot simpler to buy new mounts. they don't cost much at all.
    you can easily put a chevy 350 in there. you can buy 350 chevy mounts from pretty much any auto store (chevy 350's were used in 90-92 fleetwood broughams) you would need the pulleys for the accesories for a 90-92 350 chevy. I'm not sure if you would have to change the trans brace or not to accomodate a 700r4. but you will need to alter your driveshaft or get one for a 90-92 fleetwood brougham if you change the transmission.
    you car DOES NOT have a 200r4 (olds bellhousing 4 speed overdrive). it has a th400 (olds bellhousing 3 speed)
    IMO, upgrading to the 700r4 trans would be alot better than keeping the th400. mileage would improve quite a bit, as would acceleration.
    the fuel injection system on the V8-6-4 is unique to that motor and cannot be retrofitted to any other motor. if you want fuel injection, get a 350 tbi manifold and fuel injectors or vortec heads and intake. vortec heads and intake make good power and actually increase mileage over the older 76cc chevy heads.

  10. #9
    asaddman is offline Cadillac Owners Member
    Automobile(s): 81 Coupe DeVille
    Join Date
    May 2011
    Posts
    26

    Re: 81 Coupe DeVille Engine swap

    Totally appreciate all the feedback, much needed and appreciated!! I plan on running a carb I like them, I was just worried that maybe the fuel pressure would be deferent or it might not work at all due to if being fuel injected and I want to run a carb.

    So it sounds like if I go to the parts store and get 350 motor mounts for a 90 fleetwood I should be good to go there, and I still have all the pulleys from the 368, planning on running the ps/alt/ac hell with the emissions.

    Also looks like I need to get a 700r4 trans which I agree is easy enough to find. sven914 you think that the drive shaft would fit for it? If not I have a couple leads on custom made for a reasonable price. I also was planning on fabricating a different trans brace if the new one needs it and I want to run true dual exhaust on it.

    Again I do appreciate all the feedback.
    Attached Images

  11. #10
    cadillac kevin's Avatar
    cadillac kevin is offline Cadillac Owners Master
    Automobile(s): chevy 350 powered 86 FWB, 00 safari h.t. 66 toro, 83 lesabre
    Join Date
    Dec 2010
    Location
    St. Louis, MO
    Posts
    5,604

    Re: 81 Coupe DeVille Engine swap

    you will need chevy pulleys for the accessories. GM pulleys differed from brand to brand and are not interchangeable in my experience.
    the driveshaft is not the same length for the turbo 400 trans and the 700r4 trans. I dont remember if you will need to shorten or elongate the one you have though. finding one off a 90-92 fleetwood brougham is your best (and cheapest) bet.

    thanks for showing the pics. that car is CLEAN!!! too bad the engine blew, but it'll make an awesome cruiser when its done.
    as for the exhaust, a crossmember for a caprice should work. (I believe some companies make dual corssmembers for a caprice, but they are $$$). I'd compare bolt locations first, but they should be the same.

  12. #11
    sven914 is offline Cadillac Owners Connoisseur
    Join Date
    Dec 2008
    Posts
    4,164

    Re: 81 Coupe DeVille Engine swap

    Quote Originally Posted by asaddman View Post

    Also looks like I need to get a 700r4 trans which I agree is easy enough to find. sven914 you think that the drive shaft would fit for it? If not I have a couple leads on custom made for a reasonable price. I also was planning on fabricating a different trans brace if the new one needs it and I want to run true dual exhaust on it.
    If you get one form a '90-'92 Brougham, it will fit perfectly with the 350 and THM 700. You would only need to get one custom made if you keep the TH 400.

  13. #12
    cadillac_al is offline Cadillac Owners Connoisseur
    Automobile(s): Cadillac 78 Seville, 78 Coupe de Ville, 92 Sedan de Ville
    Join Date
    Feb 2007
    Location
    Maine
    Age
    52
    Posts
    2,710

    Re: 81 Coupe DeVille Engine swap

    Don't forget the frame mounts too. That's the funnest part of the whole swap. To do it correctly you need to remove your front suspension to get at the bolts. A lot of people cut off the old mount and weld on the new mounts to save all that labor. That's why I would let the frame mounts determine which engine i put in there. Are we sure the 368 uses Olds mounts? I kind of thought they were Chevy mounts

    OK I just took a look at my 77 Fleetwood 425 and they sure look like Chevy mounts to me. I could barely see them through just a little opening. I think you may be in bithness

  14. #13
    asaddman is offline Cadillac Owners Member
    Automobile(s): 81 Coupe DeVille
    Join Date
    May 2011
    Posts
    26

    Re: 81 Coupe DeVille Engine swap

    Quote Originally Posted by cadillac_al View Post
    Don't forget the frame mounts too. That's the funnest part of the whole swap. To do it correctly you need to remove your front suspension to get at the bolts. A lot of people cut off the old mount and weld on the new mounts to save all that labor. That's why I would let the frame mounts determine which engine i put in there. Are we sure the 368 uses Olds mounts? I kind of thought they were Chevy mounts

    OK I just took a look at my 77 Fleetwood 425 and they sure look like Chevy mounts to me. I could barely see them through just a little opening. I think you may be in bithness
    I will take a pic of the mounts today and upload them, they mount differently to the block than the 350 I got. These have 2 bolts that run through the block itself then attach to the frame motor mount, the 350 has a triangle shaped mounting area on the block that the bolts will thread into, so ya that will be a challenge but nothing I can't handle, I am not sure how I was going to tackle taking off the frame mounted mounts but if they are difficult cutting is always an option for stubborn bolts.

  15. #14
    asaddman is offline Cadillac Owners Member
    Automobile(s): 81 Coupe DeVille
    Join Date
    May 2011
    Posts
    26

    Re: 81 Coupe DeVille Engine swap

    Quote Originally Posted by cadillac kevin View Post
    you will need chevy pulleys for the accessories. GM pulleys differed from brand to brand and are not interchangeable in my experience.
    the driveshaft is not the same length for the turbo 400 trans and the 700r4 trans. I dont remember if you will need to shorten or elongate the one you have though. finding one off a 90-92 fleetwood brougham is your best (and cheapest) bet.

    thanks for showing the pics. that car is CLEAN!!! too bad the engine blew, but it'll make an awesome cruiser when its done.
    as for the exhaust, a crossmember for a caprice should work. (I believe some companies make dual corssmembers for a caprice, but they are $$$). I'd compare bolt locations first, but they should be the same.
    Dang too bad them pulleys wont work, of course I will try before I go another direction, I believe that I will probably have to get the driveline made longer but hopefully I can find something in the junkyard, wonder if the yokes will match up? As for the brace I will look into the caprice, if not I am a welder and fabricator so that stuff is the easiest part for me, its all this other nonsense.

  16. #15
    csbuckn is offline Cadillac Owners Master
    Automobile(s): 84 Coupe w/500
    Join Date
    Jan 2008
    Location
    Minneapolis
    Posts
    5,103

    Re: 81 Coupe DeVille Engine swap

    Sounds like you just need a 90-92 Brougham to use for parts. Motor, accessories, tranny, driveshaft and rearend would all be there for you. Just take off the fuel injection stuff, put a carb on and your all set.

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.
If you do not want to register, fill this field only and the name will be used as user name for your post.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Bookmarks

Cadillac Posting Rules

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
Read about Lincoln | Buick | Kia Forte Forum
Need products for your Cadillac? Check out your options at the links below:

custom floor mats | Cadillac Chrome and Black Chrome Wheels | window tinting