What mileage does your slant six powered ride get?

Slant 6 Engines

  1. dartfreak75

    dartfreak75 Restore it, Dont part it! FABO Gold Member

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    Back in 2001 my 1975 slant six dart was my everyday driver I drove it to school work etc. It was my only means of transportation for about 2 years. Back then I got an average of 18-20mpg thats driving around town stop and go while going to school along with interstate duty going to work. The best I ever got was I took it on vacation and on the way it was all interstate and I remember getting 23mpg. Shortly after that in 2003 I bought my 85 ram 318 it got about 9mpg no matter what lol. So I used to dart on nice days and the truck when it was less than perfect weather. Or i needed to haul something. And this lasted until 2004 when i sadly locked up my slant. :( I drove that 85 off and on (I always had 2 vehicles on the road) until 2012 when I got my 2001 ram and I still drive my 01 everyday.
     
  2. rumblefish360

    rumblefish360 So close, yet so far away FABO Gold Member

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    And the mileage you got with these size tires was...?
     
  3. /sixchall

    /sixchall Well-Known Member

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    Averaged as a daily driver 17-18 MPG stop and go traffic and with freeway use 22-23 MPG.thats with a car weighing around 3200 lbs. 87 at the pump.
     
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    • Princess Valiant

      Princess Valiant Duster specialist FABO Gold Member

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      Post number 15
       
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      • 66fs

        66fs FABO Gold Member FABO Gold Member

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        I have gotten high 20's maybe 30 mpg. But that was a built 170, .06 milled head with chambers within .2cc of each other, OEM 2 barrel carb and intake, MP cam, early 70's electronic ignition, and 2 1/4 exhaust and turbo muffler through the cast manifold. I think I was running 3.23 gears and an O/D manual transmission in a 64 Barracuda. Not 55 mph but definitely long highway cruise on level ground with a vacuum gage.

        Best way to get mileage from a slant is adjust the valves, bump the timing up, and adjust the carb for proper AF mix. Get rid of the small exhaust. Use a vacuum gage and let off on the gas till it just keeps speed. The factory 2 barrel carb and manifold will give better mpg and power.
         
        Last edited: Dec 29, 2018
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        • odcics2

          odcics2 Well-Known Member

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          1968 Dart, manual steering and brakes. 904 auto. Rear? Don't remember - whatever is stock... Registration said 2700 pounds.
          Had 14" tires, some type of radials back then... (early 80s)
          Perfectly adjusted valve lash. Holley Economaster 1 bbl., using the original Holley jet, which was richer than the Econo. Timing was up a few degrees, barely knocking at part throttle. Heat riser worked fine. Stock exhaust.
          Reading the plugs: All were "text book tan"
          Got 25 city or highway. Driving easy!!!

          Keep in mind that the biggest restriction in the entire system is the throttle plate!!
           
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          • PanzerschreckLeopard

            PanzerschreckLeopard Well-Known Member

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            My Valiant averages about 14mpg overall, since I daily it, and unfortunately my commute is not exactly highway....yes , technically they're all 55 or 65 mph roads, but they're only like 4 minutes each. The most I have ever gotten was 21, if I drive on the interstate for the whole tank.

            When I bought it, it had a BBD carb conversion, 205/75R14 tires, and was otherwise stock. Currently it has a motorcraft 2100 1.08, a 2" exhaust (the basic dutra type that reuses the old manifold for back half and merges into a single larger pipe), and 195/75R14 rears (apparently the store ordered the wrong ones but I didn't notice for a few weeks; oh well, that's closer to the size it came with, and the 4.5" wheels probably can't take the 205s too well anyway; I have yet to switch the rear axle to the large bolt pattern, and I'll get a less skinny wheel after that is done). Though, the "21 mpg" figure was when it still had the BBD and stock exhaust (can't remember when the tires changed), and I just haven't made a long enough trip since then.

            A904 trans and 2.76 rear.
             
          • toolmanmike

            toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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            If you are getting 21 under those conditions you are doing great. Hop in that thing and drive 55-60 for a 4 hour round trip then get back with us. I bet you'll see 25 or so. Your mileage is not ''highway".
             
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            • PanzerschreckLeopard

              PanzerschreckLeopard Well-Known Member

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              Yeah, I'd like to but I've nowhere to go that is far enough! I'd like to do the same for the Coronet for that matter ... (318, but still a 2.7X rear and I get 12.5 to 16 for the same work commute as the Valiant's 13-15. But I've never had a chance to do a long, highway trip with that car)

              I think Valiant's timing is 5* BTDC? But I have no idea what rpm it was idling at...
               
            • odcics2

              odcics2 Well-Known Member

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              The weight of the later cars kills mileage...
              My 74 Dart sucked, compared to my 68.
              My 76 was even worse... Had A/C !!
               
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              • a12

                a12 Well-Known Member

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                • 383Scampman

                  383Scampman Well-Known Member

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                  Not to throw a wrench into the works but a 318 can get just as good mileage as a / if not better . Before 2008-9 manufacturers weren't interested in mileage per se . THE sweet spot for most vehicles was 55 mph and around 1500-1700 rpm with recommended tire size . My 2000 Durango 5.9 Magnum gets 12 mpg on a good day , going down hill with a tail wind . It weighs in @ 5,240 lbs . In contrast my 2018 Ram 5.7 gets 19.4 mpg all day long and weighs 5,450 lbs. MY point is : sometimes a 6 cyl. can get less mileage than a v-8 . Fact : flathead fords only got 8-10 mpg
                   
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                  • 66fs

                    66fs FABO Gold Member FABO Gold Member

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                    4.10 gears x .73 = 2.99 or lower with .71 = 2.91 O/D. Add tall tires and the ability to tune. And if he built a 40's Dodge Coupe with /6 + O/D manual transmission and 4.10 gears, I'll bet he can tune. I can see it. I've seen too much to doubt that one.
                     
                  • kesteb

                    kesteb Well-Known Member

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                    It always amuses me when people set around and worry about the gas mileage on 50 year old hobby cars. If you want gas mileage buy a new fwd car. I did and the savings from not driving my Dodge RAM pays for the new car.
                     
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                    • Slantsix64

                      Slantsix64 Well-Known Member

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                      I call bullshit on any slant six automatic getting over 20mpg, especially in a 67 and up a body either you have a bad gas gauge, or speedos off. Best mileage would be with early a bodies with an overdrive no power anything, probably at best 22mpg. Maybe better with a 198 or 170. For me the biggest gain in fuel mileage was converting over to a 4 speed with a 225 went from 17mpg to 20mpg. I dont count my mileage from my speedo, or gauge. I carry two 1 gallon tanks of gas drive until i run out and count my mileage on gps. I bet if you guys did this you will actually see what mileage you get not just guessing and rounding.
                       
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                      • Slantsix64

                        Slantsix64 Well-Known Member

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                        My Valiant averages about 14mpg overall, since I daily it, and unfortunately my commute is not exactly highway....yes , technically they're all 55 or 65 mph roads, but they're only like 4 minutes each. The most I have ever gotten was 21, if I drive on the interstate for the whole tank.

                        When I bought it, it had a BBD carb conversion, 205/75R14 tires, and was otherwise stock. Currently it has a motorcraft 2100 1.08, a 2" exhaust (the basic dutra type that reuses the old manifold for back half and merges into a single larger pipe), and 195/75R14 rears (apparently the store ordered the wrong ones but I didn't notice for a few weeks; oh well, that's closer to the size it came with, and the 4.5" wheels probably can't take the 205s too well anyway; I have yet to switch the rear axle to the large bolt pattern, and I'll get a less skinny wheel after that is done). Though, the "21 mpg" figure was when it still had the BBD and stock exhaust (can't remember when the tires changed), and I just haven't made a long enough trip since then.
                        A904 trans and 2.76 rear.[/QUOTE]


                        Thanks for being honest, if i were you doing a lot of city driving i would swap gears to 3.23 less gas needed to get moving from a stop and still good to cruise. you might be able to get to the 17-18mpg range
                         
                      • RustyRatRod

                        RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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                        Well, here's the "THANG". TONS of people DO NOT know how to measure mileage. MPG is an AVERAGE of MANY tanks full. It is NOT a "ONE TIME" thing. You cannot just measure mileage on one tank and say "I get XX mileage". AIN'T how it works. NEVER has been. Also TONS of people "JUST SLAP" don't know how to add or subtract, either.

                        Just look at some of these new fangled modern jobs that display live MPG on the dash. I have "SEEN" dash displays show 90 plus MPG, downhill, coasting with no accelerator involved. That doesn't mean you're "gettin" 90 plus MPG. That's not how it works.

                        A LOT of people are just "SLAM IGNORANT" about how to go about figuring mileage and always will be. You caint tell them anything.
                         
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                        • Charrlie_S

                          Charrlie_S Well-Known Member

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                          Just checked the mileage on my 84 D100, on fillup, yesterday. 15.x mpg. that was just normal driving around, some hywy, some local, no interstate. The only other checks I have made was when towing my race car, which got 12-13 mpg mostly interstate.
                          Slant six, all emisions removed, super six, A833od, 3.91SG 8 3/4, 225/75-15 tires, 30 gal tank, A/C, aftermarket cruise control. Just got the truck this summer, and have no idea, what, if anything is done inside the engine.

                          I have a 64 Valiant 4dr, that was built for mileage. 170 slant six, 3sp stick, Don't remember the rear gear (2.93 I think). I does get 27-28 on the interstate. Engine was built for mileage.
                          Bored and honed .060 with a block plate, decked, balanced, Stock valves, but pocket ported, head cut for a true 9.5 CR. Mildest MP cam, and 340 springs. Windage tray, crank scraper, Stock intake and exhaust manifolds, larger exhaust pipe(s). Ign was points, but just converted to EI/HEI, which hurt. Dist curve is all wrong (need to recurve). Future plans (after some body work, rust repair) are A833od conversion, Holley economiser 1 bbl carb (and/or try some other carbs).
                           
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                          • 66fs

                            66fs FABO Gold Member FABO Gold Member

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                            I know how to calculate mpg. I had a Stewart Warner speedo and calibrated the odometer over 200 miles using the mile markers. My mpg was consistent and within a couple mpg with 300 mile tank fills. Cruising highway is the only meaningful way to check mpg. How many lights, How long at the light? Stuck behind grandma for how long?
                             
                          • a12

                            a12 Well-Known Member

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                            • Garys72Duster

                              Garys72Duster Well-Known Member

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                              I've heard of guys getting 38 Hwy with the Feather Duster. I can actually get 35 with my 300 C on the Hwy at 55 MPH. And that's got a Hemi in it!
                               
                            • Charrlie_S

                              Charrlie_S Well-Known Member

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                              Not sure what you are saying. What do you agree with and what do you think I'm lying about?
                               
                            • moparblood

                              moparblood Well-Known Member

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                              Not everyone drives the same. or have the same road conditions. i drive 160 miles a day.just bought a 76 dartlite. i'm testing these theories. owner claimed 30+ mpgs.
                              Not doing anything to the car 1 st. trip was 28 mpgs at a steady 1900 rpms. i will do a tread soon. all the adjustments tire pressure, size,etc.. to see what i can achieve.
                              Not all cars are the same either. owned 12 neons, 2 got 36 mpgs others Not so much. same motors. go figure!
                               
                            • toolmanmike

                              toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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                              Tall tires on the rear. I'll have to look next time I see the car.
                               
                            • memike

                              memike Super Moderator Staff Member FABO Gold Member

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                              I fill my tank to the brim and drive it as daily as I normally do daily, after two days I go back and fill it back up to the brim and take a look at the amount of gas it to to fill it back to the brim, take a mileage reading and do the math, then if I take a trip 200 miles or a little less, do the same, about the closest I can get.
                               
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