73 Dart /6 MPG

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Mike's Dart

Mike's Dart

Dodging The Negative Darting Toward The Positive
Joined
Nov 20, 2016
Messages
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Location
McDermott, Ohio
Finally fueled up and did the math on my first MPG check! 14.7 mpg with mostly back road driving! That is about right, eh?
 
It's not out of bounds. You'll get people claiming they got 26 mpg all day every day in their Slant-6 Dart uphill both ways in the snow with the A/C on -- those stories are mostly a mix of rosy memories and fast odometers. Your mileage will improve as you keep tuning and improving the car.
 
slantsixdan said:
It's not out of bounds. You'll get people claiming they got 26 mpg all day every day in their Slant-6 Dart uphill both ways in the snow with the A/C on -- those stories are mostly a mix of rosy memories and fast odometers. Your mileage will improve as you keep tuning and improving the car.
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I agree! Valve adjustment, wheel bearings, brake job and maybe a coat of wax! ;-)
 
Mike's Dart said:
Made me laugh out loud! :rofl:
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Not just the side glass, front & back glass and put on some good goggles!
Might as well put on some big rear shackles so you are always going down hill,
that always helps the mileage.
 
Depends how you drive it also
I've always found gutless cars harder on gas for me cause I push them harder.
 
So today I went 120 miles round trip in my '74 Duster. Surface streets, a short freeway jaunt, then highway and mountain roads, starting at a couple hundred feet elevation and driving up through 3,500 ft of elevation and then back down. I got 13.3 mpg, and that's with a 400-ish hp 340 with a 750 double pumper, 3.55 rear gears and a standard 4 speed transmission. I was not driving gently either. My odometer is actually pretty accurate, but for this particular drive it's a non-issue as I've made it many times with many cars and am quite aware of the distance (matches the GPS too). I've also made the trip frequently with the Duster, 13 mpg is pretty much spot on average for it. I've gotten close to 14 (when traffic prevents a "fun" pace through the winding roads) and as low as about 12 (when a complete lack of traffic allows a thorough flogging of the twisties), but most of the time it's right around 13.

I would hope like heck a /6 could do better than 14.7mpg . I think 26 mpg would require a tail wind, a downhill run, overdrive gears and some wishful thinking, but I would be hoping to get a lot closer to 20 mpg depending on your particular set up and gearing.
 
I carefully documented mileage in my 69 Dart 225 from 1977-95, when gas was ~2x today's price, and I used fill-up to fill-up w/ gas pump reading and validated odometer to mileage markers. I got 22 mpg hwy and ~17 mpg in combined driving. Anytime you brake is wasted energy (ask a bicyclist) and driving short distances on a cold engine is inefficient. Driving 70 mph vs 55 uses ~30% more fuel in these cars, less so w/ the lemon-drop cars of the 1990's. Even my 65 Newport w/ 383 big-block got 18 mpg hwy. In both cars changing to Crane Cams XR700 electronic ignition didn't improve mileage. In the Newport, a Holley Pro-jection 2D didn't improve mileage over the 2 bbl Rochester carb, and was always finicky.

I think your 1973 has EGR. By 1974, they had more complicated vacuum controls of spark timing and such, at least in CA cars. Either of those can reduce mileage if not working perfectly. If yours has the air snorkle diverter, insure it is working. One friend noted their Escort getting much worse mileage and poor power on a trip in the 1980's and found the diverter stuck in the "suck hot air past exhaust position". Probably made the carb run rich. Moving it manually fixed that.
 
brian6pac said:
Not just the side glass, front & back glass and put on some good goggles!
Might as well put on some big rear shackles so you are always going down hill,
that always helps the mileage.
Click to expand...
Vinyl top gotta go too!
 
Spec (TDC) is good for creating mushy acceleration and poor mileage. Try 5°BTDC with the engine idling at 600 rpm and the vacuum advance hose disconnected from the distributor and (hose) plugged. Then reconnect the vacuum advance hose and readjust your engine idle speed to 750 rpm, making sure both the idle speed and mixture are set correctly per this post.
 
slantsixdan said:
Spec (TDC) is good for creating mushy acceleration and poor mileage. Try 5°BTDC with the engine idling at 600 rpm and the vacuum advance hose disconnected from the distributor and (hose) plugged. Then reconnect the vacuum advance hose and readjust your engine idle speed to 750 rpm, making sure both the idle speed and mixture are set correctly per this post.
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I have a 73 Dart with a 71 slant six, bone stock, no emissions crap, ign timing set at 10, 2.76 gears, auto, and 205/75/14 tires. Just got back a few weeks ago from a 38 day, 8,035 mile road trip. Car loaded down with parts, tools, luggage. Lots of cold starts. Some heavy city driving (Chicago, St Louis, Albuquerque, and a 5 1/2 hour stop light to stop light grind through LA. A lot of back roads and light city driving ( I did route 66 ), over mountains and through snow (on the return trip), and some higher than normal highway speeds, for someone from the North East anyway (70 mph). Used just over 400 gallons for an mpg average of 19.8 mpg. Agree with other poster that 70 mph vs 55 uses more fuel. Also Nebraska corn bred gas may be cheaper but also causes mpg drop.
 
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