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500, 472, 425, 368 Discussion, Gas Mileage of the 500 in Cadillac Engine Technical Discussion; Originally Posted by Night Wolf 1981 commercial chassis had the DEFI 368 WITHOUT V8-6-4, I could be wrong, but IIRC ...
  1. #46
    DaveSmed's Avatar
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    Re: Gas Mileage of the 500

    Quote Originally Posted by Night Wolf
    1981 commercial chassis had the DEFI 368 WITHOUT V8-6-4, I could be wrong, but IIRC the commerical chassis kept the base 368 until the 307 was used.
    maybe somebody did a little swapping?
    That air cleaner riser looks exactly like the one on the 1981 V8-6-4 I got all the, well, V8-6-4 stuff from...
    Not quite. By the time the 307 was used, the commercial chassis moved over to the thundering beast known as the HT4100. The hearses and limos went FWD, and they were really goofy looking. Also, most hearse conversion companies switched to Oldsmobiles and Buicks at this time. Wonder why...



    Regarding the carbureted 368, I thought so, I was pretty sure the fuel injection setup was only with the DoD system... Never saw one though.

  2. #47
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    Re: Gas Mileage of the 500

    Heh, the local funeral home back in NY had a FWD HT4100 DeVille hearse... yeah, it was goofy looking... in good shape, but eh... if I was running a funeral business, I would NOT want that car.

    But the RWD commercial chassis retained the 368, even when the regular cars switched to the HT4100.... once the 307 Broughams came along, those were used..

    IIRC 1984 was the last year for the factory limo, all the factory commercial chassis from 1980-1984 got the 368. After that it was all aftermarket, and those guys used the 307 Brougham.

    In the rare case you find an aftermarket 1982-1984 DeVille streched into a limo.... it has the HT4100... that is just something to behold right there .

  3. #48
    DaveSmed's Avatar
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    Re: Gas Mileage of the 500

    Quote Originally Posted by Night Wolf
    In the rare case you find an aftermarket 1982-1984 DeVille streched into a limo.... it has the HT4100... that is just something to behold right there .
    Damn, that would redefine slow... Don't think you would find one though, as the outfitter doing the stretch conversion would almost undoubtedly opt or the heavier duty commercial chassis, thus getting the 368. I've seen the '85-up FWD HT4100 commercial chassis limo conversions though. Can't imagine they would be particularly quick or reliable either.

  4. #49
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    Re: Gas Mileage of the 500

    There was one posted on the forums not too long ago

    One of these "look at this" conversions...

  5. #50
    tricoastaljoey is offline Cadillac Owners Member
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    Re: Gas Mileage of the 500

    In response to the origonal Question..75 Eldorado/dyno tuned for 62mph/24mpg. I was in school and doing fuelsystems at the time. Daily driver(120 miles/day)with 3 buddies riding to school with me. If the 368 has a feedback carb the ground lead at the mixture solenoid may need to be connected to a temp switch in the head or block to allow it to GROUND when hot and go into closed-loop/regulated control. The default mode is wide open/RICH. That may explain the performance and mileage you are experiencing. A vacuum switch that is adjustable to open the circuit at WOT would keep the performance and allow better mileage. JOE

  6. #51
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    Re: Gas Mileage of the 500

    Thank you! I'll check that tonight.
    I might have a lead on a non-feedback quadrajet, which would eliminate the problem completely. eBay always seems to have conventional HEI distributors also, so I can get rid of 10 miles of spaghetti in the engine compartment also.

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