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500, 472, 425, 368 Discussion, Gas Mileage of the 500 in Cadillac Engine Technical Discussion; Like the Cadillac Northstar? The cylinder deactivtion (just deactivating the injectors, not the valves) was one of the big features ...
  1. #16
    BluEyes's Avatar
    BluEyes is offline Cadillac Owners Enthusiast
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    Re: Gas Mileage of the 500

    Like the Cadillac Northstar? The cylinder deactivtion (just deactivating the injectors, not the valves) was one of the big features when it was introduced. Supposed to allow you to run for some time with NO coolant!

    How many gears does that excursion have? I know the automakers have been putting more than four gears in the automatics thesedays. That could explain the good mileage and acceleration.

  2. #17
    JTraik is offline Cadillac Owners Enthusiast
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    Re: Gas Mileage of the 500

    MEGA THREAD HIJACK!!!
    Dont know jack about the northstar!

    The gas Excursions run a 4spd. and the diesel runs a 5spd.

    Gear Ratios 4-sp-------5-sp
    I------------2.71:1-----3.09:1
    II-----------1.54:1-----2.20:1
    III----------1.00:1-----1.54:1
    IV----------0.71:1-----1.00:1
    V-----------------------0.71:1

    Final Drive Ratios 3.73:1,4.10:1,4.30:1

    MEGA THREAD HIJACK!!!

  3. #18
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    Re: Gas Mileage of the 500

    The 6.8L makes similar HP to a high compression 500, and less torque. Friend's F250 6.8 weighs in around 5400 or so, which isn't too far from my Deville. I bet I'd beat him if I ran duals... (and he didn't have 4.10s)

  4. #19
    bigblockcaddy is offline Cadillac Owners Member
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    Re: Gas Mileage of the 500

    it all depends on how people keep up their car..have oil changed done often and fluids up....my 425 gets about 10/11mpg city and highway does a hole lot better it jumps to like 18/19..maybe even more depending on condition of car..but the 500 is a gas guzzler i bet i could only imagine...

  5. #20
    Chrome's Avatar
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    Re: Gas Mileage of the 500

    Ok, with all this mileage talk I'm feelin pretty bad.
    I have an 80 hearse, supposedly with the 368 (non-8-6-4).
    The folks I bought it from said it had a 400 "something" in it, kids just don't remember anyting...
    I'm lucky to get 10 mpg, it seems to be running fine, smooth, and lots of power.

    What throws me about the possibility of the 368 being replaced (the emissions sticker says 6 liter) is that is has plastic valve covers, feedback carb, computer controlled distributor.
    Is there any visual checks that I can make to be sure that is is indeed a 368? It sure seems to have a lot more power than is advertised for the 368.

    Plans for the drivetrain in this car (let me know if I'm outa line anywhere in here.)
    Dual exhaust, standard "old school" quadrajet, standard HEI, and a shift kit in the tranny (plus tranny cooler). All I want this car for is to tinker/make kinda nice, tow my 14' Shasta camping trailer (2000lbs), and for the looks I get driving down the road. So maybe even a #3 cam would be in order too... Not lookin to tear up the streets... LOL!

    Anyway, thanks for the input ahead of time, and sorry about dredging up an old thread.

  6. #21
    The Ape Man's Avatar
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    Re: Gas Mileage of the 500

    Post a picture of the engine if you can. 1980 OEM will not have a feedback carbonator.

  7. #22
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    Re: Gas Mileage of the 500

    Quote Originally Posted by The Ape Man
    Post a picture of the engine if you can. 1980 OEM will not have a feedback carbonator.
    Ok, I'll take a few pictures this weekend without the air cleaner so to see the engine better.

    Also, being that it is a hearse, Cadillac was done with it's production of the basic chassis in 1980, Superior was done with the car in 1981, and the title says 1981. So I'm not sure which emissions standards it has to live up to, or if there was a difference in carb types between the years.

    I was messing behind the glove box trying to see why the heat door wasn't working, and did find that the part of the computer harness that runs up to the dash was unplugged... I'm assuming that was not a good thing (hehehe) so I plugged it back in. We'll see if that makes much difference. I did notice in the wiring diagram that part of the harness basically just runs the check engine light and the diagnostic plug? I don't believe it actually has anything to do with the operation of the comuter does it?

    Thanks

    Tony

  8. #23
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    Re: Gas Mileage of the 500

    Grab the production date from the driver's door too. This is going to be interesting.......

  9. #24
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    Re: Gas Mileage of the 500

    Quote Originally Posted by The Ape Man
    Grab the production date from the driver's door too. This is going to be interesting.......
    Date Inc Veh Mfd 12-80
    Date of Manufacture 1-81

    Veh Type MPV

    That's about it on the drivers door tag. Unless you need part of the VIN...

    Tony

  10. #25
    STDog is offline Banned
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    Re: Gas Mileage of the 500

    Quote Originally Posted by Chrome
    Date Inc Veh Mfd 12-80
    Middle of the 1981 model year

    Rember the 81 models started production prior to the introduction (start of sales) on September 25, 1980.

    That's about it on the drivers door tag. Unless you need part of the VIN...
    The VIN will be:
    1G6AZ90, then the engine code
    "6" V8-368 4-bbl
    "9" V8-368 DFI

    I'm guessing it's a 6. The VIN is explained here about half way down the page.
    The standard engine for the CC was the V864 though. Look here, about half way down. It also stayed the CC and Limo engine through the '84 model year. Looks like it was dropped in '85, But cannot find data on the '85 CC. Did they stop the CC completely?
    I know ambulances had moved on to truck styles long ago, but what did the hearse makers use then?

  11. #26
    The Ape Man's Avatar
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    Re: Gas Mileage of the 500

    What he said. Should have 1981 drivetrain from the factory with that prod date.

  12. #27
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    Re: Gas Mileage of the 500

    But wouldn't the '81 drivetrain be the 8-6-4?
    This is a "regular" V8, computer carb and dist...
    Plugging in that part of the computer seems to have helped gas mileage a bit... Won't know for sure until I put gas in it again.

    I still need to get the heater door to switch, it's friggin cold... LOL!

  13. #28
    The Ape Man's Avatar
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    Re: Gas Mileage of the 500

    YUP '81 would be an 8/6/4 with TBI. I don't think you could get a 368 without TBI in '81 on anything AND the 368 didn't use a feedback carb any year.
    Maybe you have an Olds conversion. Those were very popular. The wiring to go from a DEFI to CCC Olds would be plenty of work though.

  14. #29
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    Re: Gas Mileage of the 500

    I'll take some pics today. It's a Caddy motor if I remember correctly. I had a '70 Fleetwood back in about '88. I believe it had the 472. The engine looks similar to what I remember...

  15. #30
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    Re: Gas Mileage of the 500

    Here are those engine pics.
    Please excuse the dirty/messy engine compartment. Haven't gotten around to getting it the way I want it yet.
    Attached Images

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