Will a 500 engine fit a 77 Coupe Deville?
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500, 472, 425, 368 Discussion, Will a 500 engine fit a 77 Coupe Deville? in Cadillac Engine Technical Discussion; I have a 77 Coupe Deville with a 425. The 425 has some somewhat serious problems with it so I ...
  1. #1
    penguinonbud is offline Cadillac Owners Member
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    Will a 500 engine fit a 77 Coupe Deville?

    I have a 77 Coupe Deville with a 425. The 425 has some somewhat serious problems with it so I would like to rebuild it. The local paper has an ad for a 500 for $300, and I would like to drop that in and use it as a temp motor while the 425 is rejuvinated. As far as I know the 500 was used from 71 to 76 so I'm not sure if it will fit into my car. Any help?


    Thanks in advance!

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    lux hauler is offline Cadillac Owners Connoisseur
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    It should be, pretty much, a bolt in. The blocks exterior dimentions are just about the same.
    You might have to use 472/500 exhaust manifolds though. I remember reading that one of the big block ex. manifolds wouldn't work on the 500......maybe it was the 368.....? Anyhow......the manifolds in question won't cover the bottoms of the exhaust ports in the heads.
    The 500 manifolds will breath a little better than the 425's will anyhow.

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    penguinonbud is offline Cadillac Owners Member
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    Re: Will a 500 engine fit a 77 Coupe Deville?

    I was thinking the two engines are the same, but I needed a confirmation from someone else

    I don't understand what you mean about the exhaust manifolds though... I'm going to use the complete 500, not part it over to the 425. Are you saying the manifolds from the 500 on the 500 might not fit the pipes, or are you saying the manifolds from the 500 on the 425 might not fit the pipes? You lost me.

    One more thing: tranny will bolt up the same, right?

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    lux hauler is offline Cadillac Owners Connoisseur
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    If you're using the 500 manifolds, what I was trying to explain doesn't matter.
    As far as I know, the exhaust pipes should line right up to the exhaust manifolds on the 500.

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    Night Wolf's Avatar
    Night Wolf is offline Cadillac Owners 10000+ Posts
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    if I were you, I would keep the 500, better then the 425, $300 is great, then build that up, if it is from the mid 70's take all the smog crap off it, then it'll be fun.....

    .....man, that is what I always want, a '77 Coupe DeVille, with a de-smoged 500 (400hp and 55ft lbs of tourqe) and build it up to be the ultimate sleeper.... it'll be great.

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    Re: Will a 500 engine fit a 77 Coupe Deville?

    Quote Originally Posted by Night Wolf
    if I were you, I would keep the 500, better then the 425, $300 is great, then build that up, if it is from the mid 70's take all the smog crap off it, then it'll be fun.....

    .....man, that is what I always want, a '77 Coupe DeVille, with a de-smoged 500 (400hp and 55ft lbs of tourqe) and build it up to be the ultimate sleeper.... it'll be great.
    LMFAO!! 55ft lbs of torque... that'd be sad. (psst I think he means 550 or 450something around there....)

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    davesdeville's Avatar
    davesdeville is offline Banned
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    Yeah that would be 550 torque, like the 70 ElDorado had.

    This should be a pretty easy swap, the engine should bolt in fine, the transmission should too. I'm almost positive the 500 exhaust manifolds will line up to the pipes.

    Read through the following link for more information than I can give you:

    http://members.tripod.com/~CadillacMan/79cadpage.html

    And why you would want to bother with the 425 once you have the 500 in there is beyond me.

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    penguinonbud is offline Cadillac Owners Member
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    Thanks a lot for the feedback, guys!

    The reason I want to use them 500 as a temp and the 425 to rebuild is because I will be doing a lot of Interstate driving in the upcoming months, and I need a reliable engine. My 425 needs a rebuilt carb (runs rich -- no big deal) but it also needs the heads rebuilt. I think the valves are sticking and letting oil through. If the heads from the 500 are good and a direct bolt on to the 425 (which I think they are), I guess I could just swap those and rebuild the 500 while driving the 425.

    Whatever, I don't care... I just want a running car

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    davesdeville's Avatar
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    The cylinder heads for the 425 are 96cc and have smaller valves than the 500's heads which were 76cc (1970-1972) or 120cc (1972-1976). I would say the 425 isn't necissarily going to be more reliable than the 500, unless you get a crappy 500, but if you're more concerned about gas mileage than you are about performance maybe the 425 is the way to go. I've heard the gas mileage for one car with a 425 is about 16/11, while I know my 500 gets about 13/9.5.

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    penguinonbud is offline Cadillac Owners Member
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    Re: Will a 500 engine fit a 77 Coupe Deville?

    I'm not saying one engine is more reliable than the other right now. The 425 is in sad shape and will get worse if I don't do something about the oil problem but I can't take it apart for more than the weekend because I need it to get back and forth to work (and school soon). Also, I may be getting a new job soon (which will be about a 50 or 60 mile round trip) so I just want something that will get me where I'm going for a month or two while I rebuild the other engine. Gas milage is no concern.

    Are the stock ratings on the 500 really 400hp and 450 to 550 torque?! That's insane.

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    penguinonbud is offline Cadillac Owners Member
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    Re: Will a 500 engine fit a 77 Coupe Deville?

    While reading around on this subject, I found a few things out:

    1.) 500 exhaust manifold clearance is a minor problem. On the right side it doesn't clear the A-frame bolt, so the bolt needs to be cut some or the 425 manifolds need to be installed.

    2.) 425 oil pan must be installed on the 500 if put into 77 Deville. (I guess because of the sump.) The dipstick tube may also need to be moved.

    3.) The brackets and pullys from the 425 must be installed on the 500. Don't know why, but they just do.


    Can anyone confirm or deny these claims?

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    davesdeville's Avatar
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    It wouldn't surprise me if all 3 of those are true, because hardly any engine swap is going to be trouble-free. As for stock hp and torque ratings of the 500, it goes down from 70 on. In the 70 Eldorado, it had 400hp/550 torque, but as they changed things to help with fuel economy and emissions, it dropped steadily until it was discontinued for the 77 model year. Also, gross hp ratings were used until 73 I believe, then the switched to net. Net is always going to be lower than gross, especially in a Cadillac, because net is measured with all the accessories on (IIRC) and at the wheels.

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    penguinonbud is offline Cadillac Owners Member
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    Re: Will a 500 engine fit a 77 Coupe Deville?

    The ad I saw didn't say what year the engine was. What year should I HOPE it is though?

  15. #14
    lux hauler is offline Cadillac Owners Connoisseur
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    The 500 was used in the Eldorado from '70-'76. It was used in all other Caddys in '75 & '76 except the Seville.
    The 472 was used in all Cadillacs from '68-'74 (with the exception of the '70-'76 Eldorado).
    Horsepower in the '70 500 was 400 gross. In '71 it dropped to around 365 due to the lower compression. The net ratings that they used starting in '71 made the hp less but just on paper.
    I wouldn't worry about what year motor you get. They can all be built to 1970 specs and make the same horsepower.....or more.
    The 425 oil pan and pick-up tube might have to be swapped over to the 500 depending on what oil pan you get with the 500......I'm not sure if the rear sump pan will work in your car. If you do use the 425 oil pan, you might have to make a little room for the rotating assembly to clear......a little bit of fancy hammer work usually takes care of that. If you use a different oil pan than what originally came on the motor, you might have to move the dipstick tube.
    The deal with the pulleys......If the motor came with an AIR pump, and you don't plan to use the AIR pump or, if you plan to use an HEI distributor on an early 500, the 425 pulleys will have to be used. The AIR pump is where you get the adjustment for your belt(s). (If you don't plan to use the 425 pulleys and want to get rid of them, let me know.....I'm gunna need a set )
    If you plan to mess with the 472/500 motors, I highly recommend the book Big Inch Cadillac. It's got lots of good info. You can get it from Maximum Torque Specialties.

    BTW.....if that 500 happens to come with a rear sump pan and you don't use it......ebay......they usually bring $100+.

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    davesdeville's Avatar
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    It doesn't make too much differance what year you get, but a 70 might save you some work on screwing with the smog equipment if you have any plans to do that. If you have an extra $250, put an edelbrock performer intake on it.

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