472, how to boost fuel economy?
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  1. #1
    3dfx is offline Cadillac Owners Member
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    472, how to boost fuel economy?

    Hi

    I have -69 De Ville. When i bought it, car was not maintained in ages and it had very bad fuel economy, 12MPG in road drive.

    Well, I replaced old airfilter and oilfilter (+oil of course) with new ones and economy went little better (13MPG).

    Is there any way to lower the MPG? I have heard some people get 17 or even 18MPG fuel comsumination? With todays gas prices (1,7€/litre here in Finland, if i calculated correctly, that would mean, 8,6$/gallon)

    Maybe I should change some ignition components such as spark plugs and breaker points. At least those looked pretty old. Are there any differences between different sparkplugs? Can I get any benefit from sparkplugs like iridium or platinum with my mechanical ignition system, or should I just buy traditional plugs like AC Delco?

    I think my ignition timing is too early (something like 30-50 degrees early). Does this effect much to fuel consume?

    Second thing is the carburetor. I think I'm going to do some mainteance in there too and change at least the float needle valve. I checked my cars emissions in local garage, and they were very nice, so air/gas mixtures are fine. What other things I should change there?


    Are there any other things what would affect to fuel economy? I dont have EGR, Pulse air systems or any other emission control equipment.

    PS. Sorry if my english was bad

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  3. #2
    j2rossit is offline Cadillac Owners Enthusiast
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    Re: 472, how to boost fuel economy?

    Welcome to the forum.
    What kind of driving are these values calculated from?
    12-13mpg city driving would be fantastic.
    if it's on the highway, what speed? What are your driving habits?
    How are the tires? bald or low pressure tires use a lot more gas.
    Timing will most certainly affect fuel efficiency.
    If your ignition components look old, they would be one of the first things I'd replace regardless of efficiency considerations.

  4. #3
    bigm57ict's Avatar
    bigm57ict is offline Cadillac Owners Connoisseur
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    Re: 472, how to boost fuel economy?

    You may be able to achieve small improvements in fuel economy, but for the car you have, 12-13 is about normal.
    By all means, perfect the timing, tire pressure, etc, but don't expect great gains from it.

  5. #4
    drmenard is offline Cadillac Owners Enthusiast
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    Re: 472, how to boost fuel economy?

    I am a old school type of guy. And a lot of guys with these motors use old style copper plugs, and I did for many years... But a year and a half ago I put in a set of denso iridium... They have been working great and would recomend using the denso plugs...I would also recomend a HEI distrubtor with the vacume advance hooked direct to manifold vacume.. do not go through the temp switches.. Make sure that the distrubtor weights are free and working correctly.. I would set the timing like this... disconnect vacume advance vac hose... rev the motor to 2500rpm or till you are at max centrifical advance and setr te timing to 35 degrees... If it pings back it off till it stops... but with 93 octane it should be ok.. If you are forced to use 87 octane it is going to be very hard with a carb... A bit eazier with fuel injection..

  6. #5
    talismandave's Avatar
    talismandave is online now Cadillac Owners Master
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    Re: 472, how to boost fuel economy?

    Drive downhill?

    Actually 12 -13 sounds pretty good as the guys were saying. If you know someone who go 17 I would doubt he was being honest with you. Or he had a different newer car with an overdrive transmission.

  7. #6
    77CDV's Avatar
    77CDV is offline Cadillac Owners Master
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    Re: 472, how to boost fuel economy?

    On the open highway, in perfect tune and under optimal conditions, your car will *maybe* hit 16mpg. In mixed driving, 12-13mpg is pretty standard. Fuel efficient, these cars are not.

  8. #7
    carnut is offline Cadillac Owners Master
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    Re: 472, how to boost fuel economy?

    All you can do is make sure the tires are at proper pressure, points and vacuum advance are new, distributor weights free. Points dwell at 30 degrees. Timing at spec or 2 degrees advanced. Wheel alignment to spec. Drive like you have an egg under your foot! If the smog readings are good then the carb float and needle and seat are good. Make sure the 4 bolts holding the carb are tight, most are 2 turns loose. You will get many opinions regarding spark plugs. In my opinion, use A/C Delco's as recommended.

  9. #8
    Aron9000's Avatar
    Aron9000 is online now Cadillac Owners Master
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    Re: 472, how to boost fuel economy?

    12-13mpg sounds about right for that engine. Also keep in mind that you need to put a lead additive in the gas if the car still has its original valve seats. I know if you ever have the heads rebuilt they'll put in hardened valve seats like modern cars have so it will run fine on unleaded gas.

  10. #9
    CADforce69 is offline Cadillac Owners Connoisseur
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    Re: 472, how to boost fuel economy?

    I have a '69 Sedan de Ville: New tires with right pressure, new points, sparks, rotor, points, distributor cap... The best mileage I did is 11 mpg during my first travel from the city I bought it to home. 80-90 Kmph. before changing all the components above mentioned. Now at 100-110 Kmph never better than 10 mpg. (Sorry, I canīt enjoy it going slower )

    Things I could improve on my car: better spark plugs (Now I have Motorcraft, that I donīt think are the best for this car) and carburetor, though I donīt have any driving or starting problems with it, but the mechanic advised me to change it when I can afford it.

    I know itīs hard driving these cars here in Europe: 1.37 € / Liter in Spain but lower salaries (and keep lowering due to the rampant crisis).

    Welcome to the forum and please, upload some pics of your car. This is my resto thread: http://www.cadillacforums.com/forums...storation.html You may take a look when you have some time

    By the way, You can rent your car for weddings or other events. That way you will drive your caddy on these occasions without any worry about mileage. Some weeks ago I did 225 kilometers during a wedding transportation. Gas paid and some profit to help maintenance
    77CDV, 77CDV, talismandave and 3 others like this.

  11. #10
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    Cady70 is offline Cadillac Owners Member
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    Re: 472, how to boost fuel economy?

    Pull the motor out and put it into a Honda Civic. You might pick up a few MPGs.
    Maybe you could pull off the quadrajet and put a 2 barrel carb on.
    CADforce69 and CADforce69 like this.

  12. #11
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: 472, how to boost fuel economy?

    Quote Originally Posted by Cady70 View Post
    Pull the motor out and put it into a Honda Civic. You might pick up a few MPGs.
    Maybe you could pull off the quadrajet and put a 2 barrel carb on.
    You have to realize these are heavy cars and the engine produces the torque necessary to move it smoothly, with little effort. The Rochester Quardrajet front two venturi are most efficient and offer better fuel economy than most 2 bbl carbs on the market. In fact the two rear venturi are only in use on demand, when the air flow exceeds the capacity of the front venturi. They are subject to wear at the main throttle shaft bores.
    To check throttle shaft bore wear, remove the air filter and with the engine at idle, gently lift the main throttle shaft on the driver side of the carb at the lever for the throttle linkage. If worn excessively, the excess air drawn in arount the shaft and bore may cause the engine to lean out. If there is little free play here, your carb body/shaft is in good condition.
    The Ape Man and The Ape Man like this.

  13. #12
    Alscad56's Avatar
    Alscad56 is offline Cadillac Owners Fanatic
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    Re: 472, how to boost fuel economy?

    If you want to keep the original engine, in my opinion, the only way to significantly increase gas mileage is to get a transmission adapter for your engine, and bolt up a 700R4 automatic transmission behind it. That way, you'll at least get overdrive. That should bring up the mileage a few notches.
    My 1956 Cad has one and I get between 19-21 mpg/ highway driving...and this car weighs over 5000 pounds.

  14. #13
    cadillac kevin's Avatar
    cadillac kevin is offline Cadillac Owners Master
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    Quote Originally Posted by Alscad56
    If you want to keep the original engine, in my opinion, the only way to significantly increase gas mileage is to get a transmission adapter for your engine, and bolt up a 700R4 automatic transmission behind it. That way, you'll at least get overdrive. That should bring up the mileage a few notches.
    My 1956 Cad has one and I get between 19-21 mpg/ highway driving...and this car weighs over 5000 pounds.
    Thats pretty good mileage for a large vehicle. Wonder what mileage a 500 would get with an overdrive trans.

  15. #14
    Fleet's Avatar
    Fleet is offline Cadillac Owners Enthusiast
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    Re: 472, how to boost fuel economy?

    Motor Trend's test car (a '69 Coupe de Ville) gave 9.2 to 11.8 mpg. The low figure was obviously recorded during acceleration tests and the high figure was probably mixed driving but not 100% highway driving.
    CADforce69 and CADforce69 like this.

  16. #15
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    jayoldschool is offline GM RWD V8 addict
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    Re: 472, how to boost fuel economy?

    Quote Originally Posted by Alscad56 View Post
    If you want to keep the original engine, in my opinion, the only way to significantly increase gas mileage is to get a transmission adapter for your engine, and bolt up a 700R4 automatic transmission behind it. That way, you'll at least get overdrive. That should bring up the mileage a few notches.
    My 1956 Cad has one and I get between 19-21 mpg/ highway driving...and this car weighs over 5000 pounds.
    This will not work without changing the rear gears. The gears are very high (low numerically), so OD will be useless. Cadillac was already doing everything they could to get mileage out of their cars by this point. The 56 Cad benefited because it has a gear set in the mid 3s, while the car in question will have a low 2 gear set.

    In my opinion, just make sure everything is in top running order. It is good that you can have your exhaust gas emissions monitored, this will greatly help with tuning. Fresh plugs, properly gapped, wires, cap, rotor, set timing. If still running a cat (and in Europe, I suspect you are), you will see a benefit to going to a modern monolith cat instead of the old restrictive pellet type. A little more efficiency can be gained by a freer flowing exhaust. If you can't do full duals, you can do a very nice two into one into duals:



    The best to hope for

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