500 Caddy motor in 81 fleetwood?
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500, 472, 425, 368 Discussion, 500 Caddy motor in 81 fleetwood? in Cadillac Engine Technical Discussion; Ok.... I've read up a little on these 500 caddy motors, after hearing so much about them on this forum, ...
  1. #1
    Caddy_freak's Avatar
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    500 Caddy motor in 81 fleetwood?

    Ok.... I've read up a little on these 500 caddy motors, after hearing so much about them on this forum, and so given the chance, I bought one!

    I got motor/Tranny/Carb, everything I can strip from under hood for $200

    it's in a 76 Fleetwood, I think that's what he said. back end of car been wrecked, motor runs!

    I will have to remove it myself and I want to know a few things.

    First I'm thinking of putting it into my 1981 Fleetwood, that now has a
    368 V8-6-4 motor in it. I plan on removing 500 engine and tranny all in one piece from donor car, but it may be a few years until I'm ready for swap. as there is really nothing wrong with my 368, it runs great! and I want to rebuild both the 500 and the TH400 before the swap! are there any other parts (brakets/mounts/or what ever) that I will need From the donnor that are not obvious? few years down the road donner car might be (gone/crushed/stripped)

    Also I read on this forum that 500 block and my 368, = same block dimentions on outside, but how about mounting A/C and t other stuff? Exaust/ fuel mods? how about motor mounts? I know some of you here have allready putt 500 motor in a newer Caddy and I'd appreciate some advice.

    Now as far as building the motor itself, I'd like to end up with a streetable motor that will run well on premium (pump gas) maybe a little bit of cam but streetable! like a vt3 reground from MTS? lots of low end torque good fuel mileage. cast or forged pistons? how about heads? what mods should I do to them in the machine shop? what comp ratio should I consider?

    Also what about once it's done? will I rip the rear end out of my car? these 81 fleetwood's do they have a semi/strong rearend? these 500 motor I'm told have Torque with a capital "T" (500+). I also read that the 500 likes to pull better than rev, again.....lot's and lot's of torque! and that I should gear the rearend to suit the carecteristics/preference of the new motor, for longer engine life, what gears would be proper?

    And lastly, are there any specific books/publications I should read to help me learn about this motor/project more,

    I'd like to inform/educate myself before I spend money at the machine shop or the parts store.

    I'd apreciate any advice/help i can get, oh great Caddy Gurus!

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    MMNineInchNails's Avatar
    MMNineInchNails is offline Cadillac Owners Enthusiast
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    Re: 500 Caddy motor in 81 fleetwood?

    From reading all the other posts with the 500s, I do think you need the motor mounts. I'm not positivly sure but I don't think the exhaust will fit all the way. dunno though wait til someone else responds.

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    Caddy_freak's Avatar
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    Re: 500 Caddy motor in 81 fleetwood?

    Thank's,

    I remebered that also forgot to ask another question about this swap.
    What about those air polution Nazis? What will the Gestapo do when it's time for the sniff test?

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    Ultra Slow is offline Cadillac Owners Fanatic
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    Re: 500 Caddy motor in 81 fleetwood?

    Yes the motors are the same. There are about 1/2 dozen things you will need to modify to do it, none hard. Just take EVERYTHING from the 368... Mounts, brackets, etc and put on the 500. If you are a "PC" polution guy, the 500 will work with that too if you put a cat, aire pump, etc on it. If you are looking for performance, there are some things you should do to that 500 before you put it in the car as you will wish you did it later if you dont now... Intake is one for sure.


    Cad 500 Site


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    Re: 500 Caddy motor in 81 fleetwood?

    well I went back to that MTS site www.500cid.com and found some good reading about the 500 Caddy motors that I had somehow missed on my first visit there.

    OK ultra slow. so you say my motor mounts and a lot
    more can fit on the 500, that's good news. does that
    include the distributor ? (electronic ingnition vs points)
    if so that save me $$$$$ right there.


    after reading those tech articles on MTS web site. I am better able to describe what I want to build.

    I would like to build a sleeper. Car look's normal, but chalenge it to a race and That big old boat might just smoke you.

    I want to be able to run 92/93 octane pump fuel. That is the one major requirement. short of that I'm open to anything.

    Later on some nitrous, and possibly an aftermarket fuel injection system.

    but first things first. I'm not PC. I hate PC. but the state I live in is run by a bunch of Nazis. most states, at least I'm told. is that after a car has reached a certain age has no sniff test requirements.

    That could be bull %$#@ for all I know, but in North Carolina, but I'm told they will sniff test anything that's 71 or newer.
    No pass? no drive!

    I don't want to build all this and not be able to drive my car on the road anymore. if anyone has info on this I'd really apreciate it

    Now when motor first goes into car it will be carburated. also 90% of driving will be cruising/travel. only 10% racing.

    I need to build a dual purpose motor, with out getting too exotic.
    in order to run nitrous later will I need to run forged pistons in rebuild? rods too?

    if I need them I'll buy them. what ever it takes I'll do.
    this is no weekend project, if it takes a year that's fine as long as I do it right the first time!

    how about compression? I was under the impression that 10-1 was as hight as practical for 93 octane fuel. but one guy was arguing that you could go up to 12-1, he is a Diesel mechanic, I'm a shadetree mechanic. I still don't know who's right!

    and then there's the rear end, if I build a Torque Monster and put it in my 1981 Fleetwood, Can I expec to rip the rear off the car the first time I floor it? and for racing? I beleive that it's not posi trac. what should I put back there that would be bullet proof? what about the drive shaft and u joints?

    Can I modify the rear end off of the 76 fleetwood to fit my car? is it practical, or even a good idea?

    Oh by the way that picture is sharp, man that's nice

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    Re: 500 Caddy motor in 81 fleetwood?

    Hey dude! I just now found the link you put on your post above for the 500 caddy site. sorry

    Serious brain fog. man not enough sleep I guess

    It would have saved me lots of typing.:banghead2

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    Re: 500 Caddy motor in 81 fleetwood?

    Quote Originally Posted by Caddy_freak
    I need to build a dual purpose motor, with out getting too exotic. in order to run nitrous later will I need to run forged pistons in rebuild? rods too?

    if I need them I'll buy them. what ever it takes I'll do.
    this is no weekend project, if it takes a year that's fine as long as I do it right the first time!
    You shouldn't need forged pistons unless you're planning to run much more than a 150 shot. As for the emissions testing shizzle, call your local motor vehcile division. Here in Bernalillo county (the only place in NM that requires testing), the cutoff is 75.

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