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  • Poor Gas Mileage - HELP

    I have an early 1962 GT Hawk with 289, FOM, TT (3.31), 2bbl with 119,000+ miles. After checking gas purchases and mileage on the odometer I find I am getting overall 10 MPG. The engine has good compression (160 - 135), a rebuilt (T-bow) carb, Pertronix ignition module in the Delco-Remy distributor, new cap, rotor, wires, plugs and fuel filter from SI. I am running with an electric fuel pump. What can I do to improve the mileage?
    Peter Bishop
    Director,
    Northeast Zone

  • #2
    quote:Originally posted by PeterHawk

    I have an early 1962 GT Hawk with 289, FOM, TT (3.31), 2bbl with 119,000+ miles. After checking gas purchases and mileage on the odometer I find I am getting overall 10 MPG. The engine has good compression (160 - 135), a rebuilt (T-bow) carb, Pertronix ignition module in the Delco-Remy distributor, new cap, rotor, wires, plugs and fuel filter from SI. I am running with an electric fuel pump. What can I do to improve the mileage?
    Do you have a pressure regulator on your electric pump setup? It may be pushing too much gas through.



    Paul Johnson, Wild and Wonderful West Virginia. '64 Daytona Wagonaire, '64 Daytona convertible, '53 Commander Starliner, Museum R-4 engine, '62 Gravely Model L, '72 Gravely Model 430

    Paul Johnson, Wild and Wonderful West Virginia.
    '64 Daytona Wagonaire, '64 Avanti R-1, Museum R-4 engine, '72 Gravely Model 430 with Onan engine

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    • #3
      Make sure your vacuum advance is working properly. Its job is to improve fuel mileage by giving an additional 15 degrees (or so) of advance under light throttle (high vacuum) conditions.

      Check your initial advance also. If you can crank on a few more degrees than the book says and not have it ping, that will help.

      Also keep in mind that pushing around a 3200 pound car with a motor design from 1950 and with a relatively low (by today's standards) rear end and an automatic that is not real efficient and without a lock up converter, is not going to yield great mileage (despite stories to the contrary ). With everything working correctly and under NORMAL driving conditions (and with an accurate speedometer/odometer), you probably should expect low teens around town and high teens at a steady 60-65.

      Dick Steinkamp
      Bellingham, WA

      Dick Steinkamp
      Bellingham, WA

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      • #4
        Might want to check your heat riser to see if it is free. Also is there any black smoke from tailpipe?
        Frank van Doorn
        Omaha, Ne.
        1962 GT Hawk 289 4 speed
        1941 Champion streetrod, R-2 Powered, GM 200-4R trans.
        1952 V-8 232 Commander State "Starliner" hardtop OD

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        • #5
          Well...the truth...rebuild the engine.

          135 to 160 really isn't very good IF..you are looking for power AND/OR milage. I'd bet the leak down numbers are even worse.
          I've worked on many cylinder heads over my 55+ years. One thing I've noticed, no matter how well the engine is taken care of, the valve grind effency starts to dwindle after about 35,0000 miles. This goes with the leak down numbers, that ever so slightly, the valves start to leak.

          Also, the leak down numbers.....depending on how well the ring seal was when new....how the ring seal is now.
          IF..the rings only sealed enough to achieve a 4% leak down when new...you may have more like 20% leak down now, which is ...not good.
          In the earlier years, even the mid 60's, factory ring seal wasn't as a prime concern as it is today. Cylinder walls are honed better, and to better match the type of ring that is to be installed. The rings are of better material...etc., etc.

          Another thing to think about...a 4 barrel carburetor CAN, obtain better milage than a two barrel. They normally have smaller primary throttle bores than most two barrels. It is easilly possible to get notablely better milage driving carefully with the four barrel.

          And as for the two barrel and the electric pump...what Paul says is very true. Most pumps will put out much more than advertized pressures. A gauge and regulator is almost always required to make sure you are not overtaxing the needle, seat and float.

          What can you do -
          1. A quality rebuild
          2. A little cylinder head port work
          3. Good quality rings
          4. Carefull ring installation (hone quality, end gap, etc.)
          5. Compression ratio that goes with the gas you have in your area and your altitude
          6. Carefull engine assembly
          7. "Possibly" a rear end gear ratio change...depending on how and where you drive

          Well that's more than a few things to think about.

          Mike

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          • #6
            Mike is absolutely correct about your engine being tired and a rebuild is the answer. Well, yes, no and maybe.

            FWIW, most of us will never drive a Stude enough miles for an engine rebuild or rear gear swap to pay for itself in fuel economy improvement savings. However, the increased performance is worth the cost to many of us.

            If it were my car, I'd go through the ignition system. First, as Mike said, have the distributor checked on a machine.

            Check the speedometer and odometer for accuracy. Most Stude odometers, due to oversized tires, are recording fewer miles than actually traveled. Many GT Hawks I see are running tires two or three sizes too large. Not only do they cause the odometer to read wrong, they increase drag. You do have radial tires, don't you? Good quality, correctly-sized tires are important, as is an accurate front end alignment. Even slightly worn tie rods, because Stude uses so many of them, can cause the front tires to drag at road speeds. The Stude OEM recommended air pressures were for bias ply tires. Most of today's radials need 35 PSI+. Check the manufacturer's recommendations.

            Bottom line, get all the systems at maximum efficiency and enjoy your beautiful ride without worrying about the tenths of a MPG.

            thnx, jack vines





            PackardV8
            PackardV8

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            • #7
              In addition to the already mentioned things to check...Brakes!...make sure they are adjusted properly and not dragging. A slightly dragging brake or bearing can scrub significant mileage performance from your vehicle.

              John Clary
              Greer, SC

              Life... is what happens as you are making plans.
              SDC member since 1975
              John Clary
              Greer, SC

              SDC member since 1975

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              • #8
                All good replies and ideas.

                Have you verified that the odometer is accurate? I have seen more than one old car with an inaccurate odometer. You can search out the mile markers, or check an Internet map between points and see how well your odometer agrees.

                Even with modest compression and questionable leak down I would expect more than 10 mpg. A 3,200 lb car is hardly a big fat pig.

                On older cars I have usually found most of the low mpg's to be distributor related:
                1) broken/leaking vacuum advance (includes broken vacuum hose or pipe).
                2) stuck advance mechanism that does not allow for full advance.
                3) using wrong timing mark / innaccurate timing.

                A broken vacuum advance usually wastes about 2 mpg.

                Many seldom driven old cars have dragging brakes - sometimes wheel bearing problems too.

                If everything checks out good and you want to drive your GT Hawk all the time, then a chassis dyno session (warning: not CA$O friendly) may quickly find the culprit. Done properly a chassis dyno tuning session allows you to check air fuel ratio and actual ignition advance under dyno simulated road conditions.

                Thomas

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                • #9
                  Turn your idle mixture screws in until your rpm begins to drop or you hear stumbles in your idle and then turn them out until it levels out.

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