Swapping My 1980 368 to a 1975 500 This Weekend
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500, 472, 425, 368 Discussion, Swapping My 1980 368 to a 1975 500 This Weekend in Cadillac Engine Technical Discussion; Welllll. I've been sitting on this 500 for years. Freshened it up back in 1997 or so. At that time ...
  1. #1
    The Ape Man's Avatar
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    Swapping My 1980 368 to a 1975 500 This Weekend

    Welllll. I've been sitting on this 500 for years. Freshened it up back in 1997 or so. At that time I fitted it into a 1982 SDV. Long story short I will be removing my 71,XXX mile 368 in my 1980 Fleetwood 2 door and replacing it with the 500 this weekend. The 500 is all factory and has 4K miles since tearing it down. At that time the cylinder walls were perfect.

    I'll be looking for a new home for the 368. It does have one snapped exhaust manifold bolt. Otherwise it just needs rocker cover gaskets and a paint job.

    I'm keeping the carb though : )

    Maybe I'll snap some pix.

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    drmenard is offline Cadillac Owners Enthusiast
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    Re: Swapping My 1980 368 to a 1975 500 This Weekend

    You will be looking for a posi rear or buying stock in a tire store.. Whats your plans on a exhaust system? I have a 472 in my 81 SDV for over 10 years.. I'm sure you know about cutting the A frame bolt to get the exhaust manifold on, but one thing I did was mill the landing down so to use a shorter bolt in the first hole.. This makes it so you can get that bolt in and out without jacking the motor up.. I also got a great aluminum 3 core radiator on ebay, helps keep it cool...

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    The Ape Man's Avatar
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    Re: Swapping My 1980 368 to a 1975 500 This Weekend

    Quote Originally Posted by drmenard View Post
    You will be looking for a posi rear or buying stock in a tire store.. Whats your plans on a exhaust system? I have a 472 in my 81 SDV for over 10 years.. I'm sure you know about cutting the A frame bolt to get the exhaust manifold on, but one thing I did was mill the landing down so to use a shorter bolt in the first hole.. This makes it so you can get that bolt in and out without jacking the motor up.. I also got a great aluminum 3 core radiator on ebay, helps keep it cool...
    I have a 2.21:1 posi rear axle from a '78 Coupe D'elegance which I may use. It lived under my '77 CDV from 1984 to 1992 and my '83 CDV from 1992 to 1994. Had 500s in both these cars. '83 was destroyed in an accident. Mr. Allstate paid me top dollar for it as it was the other driver's fault.

    This is only stage 1 of the work. The car will remain usable. I also have a 4L80e with diesel controller and an electronic speedo head from a '92. I bought a few gearsets off ebey to try fitting into the 2.21 but I'm not sure how that will work out. One is a 2.73.

    30+ years of collecting car parts.

    There's an exhaust shop that did some great work on a friend's car at a good price. I'm just going to send the car there and get whatever he can fit in the way of duals with converters. No Monte Carlo crossmember though. I wish I could get one in a hurry.......

    Been cutting A arm bolts for many moons. Works OK. I don't use exhaust manifold gaskets on these as the designers intended. Interesting idea on grinding.

    I put a new radiator in this car in 2004 and expect it to still act new. Otherwise I'd be interested in yours.

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    drmenard is offline Cadillac Owners Enthusiast
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    Re: Swapping My 1980 368 to a 1975 500 This Weekend

    I have a posi that was ot of a 77-79 ... Don't know what year it was.. But I got 2.56 gears in it now.. Thats the lowest gears that fit into that 2.21 carrier... lower gePDC_2475.JPGars could go in if a spacer was used.. Don't know anyone that makes a spacer..

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    The Ape Man's Avatar
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    Re: Swapping My 1980 368 to a 1975 500 This Weekend

    Nice picture. I cut my bolt with a hacksaw blade and nothing else. I have a lot less shims and more clearance. I'm thinking adding more camber would move the A arm mounting even further away.

    Great catch in the posi! 2.56 has got to be next to impossible to find. Even the change from 2.21 to 2.56 would wake things up with all the torque from the 500.

    I put a 425 in an '85 Fleetwood a long time ago and left the original rear axle in for a few weeks. That car FLEW and got 13 MPG with the wind behind it.

    I need to hit the books once more and see what options there are for rear axles. I still have the TH-400 and am not planning on playing with that right now. Probably just drop the 2.21 drum to drum in and call it a year.

    I purchased a Megasquirt board and still have a 425 F.I. intake. I'd like to get all that stuff working someday. I have an original 500 EFI ECM but not the injectors. I'd like to find injectors which will work in that manifold using the Megasquirt. Then again it would be nice to adapt a 460 manifold with it's long runners. I doubt it would fit under the hood though.

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    drmenard is offline Cadillac Owners Enthusiast
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    Re: Swapping My 1980 368 to a 1975 500 This Weekend

    The stock injectors are low ohm.. They need add on drivers and megasquirt has some that will drive them...I have some used injectors if you ever get around to going that way... My 472 is injected with stock parts and a haltech running it...

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    The Ape Man's Avatar
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    Re: Swapping My 1980 368 to a 1975 500 This Weekend

    Quote Originally Posted by drmenard View Post
    The stock injectors are low ohm.. They need add on drivers and megasquirt has some that will drive them...I have some used injectors if you ever get around to going that way... My 472 is injected with stock parts and a haltech running it...
    Thanks for the offer. Do modern garden variety injectors fit physically in the old manifold? What's a Haltech. I'm a dinosaur.

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    Re: Swapping My 1980 368 to a 1975 500 This Weekend

    There are many different injectors and not sure what fits... But I'm betting you won't find any to fit without machining...A Haltech is a aftermarket computer that you can tune the car with a laptop...

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    Re: Swapping My 1980 368 to a 1975 500 This Weekend

    OK. Thanks. The Megasquirt is the same idea. Your's is probably more advanced than what I have. Mine is 7 or 8 years old.

    Quote Originally Posted by drmenard View Post
    There are many different injectors and not sure what fits... But I'm betting you won't find any to fit without machining...A Haltech is a aftermarket computer that you can tune the car with a laptop...

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    drmenard is offline Cadillac Owners Enthusiast
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    Re: Swapping My 1980 368 to a 1975 500 This Weekend

    One thing you should try to collect if you plan on doing fuel injection is a 1981 -368- 4-6-8 F/I distrubtor...

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    Re: Swapping My 1980 368 to a 1975 500 This Weekend

    Quote Originally Posted by drmenard View Post
    One thing you should try to collect if you plan on doing fuel injection is a 1981 -368- 4-6-8 F/I distrubtor...
    For the module?

    I have the old reed switch distributor from a 425 and don't like the idea of using it........

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    drmenard is offline Cadillac Owners Enthusiast
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    Re: Swapping My 1980 368 to a 1975 500 This Weekend

    you don't need that old distrubtor. the 81 has a 7 pin module and can be used with all systems that control timing..

  14. #13
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    Re: Swapping My 1980 368 to a 1975 500 This Weekend

    Yes, I do not want to rely on the reed switches. Isn't the module out of an HT-4100 car the same as the '81? Out of all the junk I've saved I never thought to save either one of those : (

    Got the engine running last weekend. Monte Carlo cross member showed up from the UPS man today. Need to bring it to the exhaust guy for duals next.....

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    drmenard is offline Cadillac Owners Enthusiast
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    Re: Swapping My 1980 368 to a 1975 500 This Weekend

    The module is the same from the 4100.,. But the distributor from the 81 a bolt in.. If you try to use a dis. with a vacuum advance you can run into problems.. First of all it has to be locked down so there is centrifical or vacuum advance.. If it is not locked just right it will through off the rotor phasing.. So the best thing to do is get a 81 dis.

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    Re: Swapping My 1980 368 to a 1975 500 This Weekend

    Not sure about how rotor phasing could be taken care of since all these distributors can be rotated within the block. Mine is stuck in place. I hope it works itself loose after a few hundred miles of oil splashing around. It's only been in there since 1999 or so. Had one get stuck many years ago and it came out in pieces.

    Long time ago I had a situation where I wanted to lose the mechanical advance. Probably just brazed the parts and took off the springs/weights.

    Thanks for the heads up on those modules.

    I'll get some pix up soon.

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