Gas mileage 225 Slant 6

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Princess Valiant said:
I consistently get 16 mpg with my slant in a 68 dodge dart 2 door H/T with a 1976 OD 833.

I am kinda a lead foot and with a slant you have to be a lead foot to push it to keep up with today's traffic.

Don't expect much from a slant, sure it's only a six cylinder but it's also a heavy and very old engine that was designed to run at 55 mph or less, more so on the less part.
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You should be better than that with an OD 833. Going from a 1bbl to a 2bbl, running HEI ignition and opening the exhaust to 2 1/4" took me from 15mpg to 21mpg and that's averaging 75mph on the freeway without traffic.

It's still a slug compared to newer vehicles but the 2bbl actually helped me keep out of the gas as hard.
 
I daily drive my 73 Dart (Known as the Shart because Stretch has a Dart :D).

I live in a very rural area of upper Michigan so my daily commute is a combination of back roads and 2 lane highways with 55 M.P.H. being the max speed. Its about 25 miles to work with two small towns to slow down through. I average 21 M.P.G. back and forth to work and on a recent road trip (200 miles round trip on two lane highways) I averaged 29 M.P.G..

My car is a 225/904 with unknown gears, 4 wheel manual drums and 14 x 5.5" wheels. I rebuilt the carb, adjusted the valve lash, did a basic tune up, replaced all the vacuum lines and replaced the intake/exhaust gasket. I set the base timing at 12 deg. BTDC. I custom bent a 2 1/4" dual exhaust system with two cheap reverse flow "turbo" style mufflers. I made a new down pipe and installed a "Y" to split to the duels. I also set the wheel alignment at .5 deg. negative camber (both sides), as close to 3.0 deg. positive caster as I could get while keeping the camber at .5 negative, and set the toe at 1/8" in.
I have collected the parts required to convert it to a A833OD this winter. I just need to rebuild the transmission and find a flywheel. It will be interesting to see what the OD does to the fuel mileage.
 
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Princess Valiant said:
I consistently get 16 mpg with my slant in a 68 dodge dart 2 door H/T with a 1976 OD 833.

I am kinda a lead foot and with a slant you have to be a lead foot to push it to keep up with today's traffic.

Don't expect much from a slant, sure it's only a six cylinder but it's also a heavy and very old engine that was designed to run at 55 mph or less, more so on the less part.
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Motor trends lil replace the stock exhaust with 2 1/2" pipe added 9 rwhp. I did that & now I dont have any issues merging into freeway traffic.

Back on the Tune Time Performance dyno revealed we picked up 9 rwhp and 10 lb-ft at peak. Maximum peak horsepower moved up from 2,900 to 3,500 rpm. Peak torque stayed at 2,900 to 3,000 rpm. Each pull was made from 2,500 to 4,200 rpm
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Making Slant Six Sense
 
That MT article is cool. Not as cool as the "weight reduced" left side frame rail though! They are amazingly easy to change. Perhaps MT could do that for one of the features on that cool little early Dart.
 
Blainethemono said:
Motor trends lil replace the stock exhaust with 2 1/2" pipe added 9 rwhp. I did that & now I dont have any issues merging into freeway traffic.



Making Slant Six Sense
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And that's a true better than 10% improvement, how 'bout that? Lol! I know the factory tailpipe on both My '64 GT's were 1.75" & the ID'S were barely 1.5" in the bends, sad really..
 
I found it depends on how I do the math. I milled the head .100", built some tube headers along with some other minor mods and got 32 MPG doing the math in my head. Put a pencil to paper and it was 22 MPG. So, in thinking about what I just said, I'd say it all depends on how I feeel about my MPG instead of actual mileage. I feel much better when I calculate the mileage in my head.
:lol:
 
Duggie said:
I found it depends on how I do the math. I milled the head .100", built some tube headers along with some other minor mods and got 32 MPG doing the math in my head. Put a pencil to paper and it was 22 MPG. So, in thinking about what I just said, I'd say it all depends on how I feeel about my MPG instead of actual mileage. I feel much better when I calculate the mileage in my head.
:lol:
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:rofl:
 
Since I've had the hot motor in Vixen a while now, I have a good sense of the mileage. She actually gets decent to have such a big cam and 4 barrel. It's probably the compression. She varies between 16 and 19 depending on how I drive her.
 
When I had my 79 d100 short bed with the slant 6, 3 on the tree manual steering and brakes and 3.55s out back// that must not have been a Monday morning or Friday night build because that thing would hit 22 mpg on a solid highway run. It would do 18-19 in mixed town/highway driving quite repeatedly. I hope I can get at least close to that with this 85. The 79 was stone stock just well maintained. This 85 is built up a little but not crazily so. .I know I'll pay a small penalty by retaining the 727 at least for now,. I may eventually either experiment with the A500 I just got (if I can find a SB trans adapter that I can afford) or else maybe convert it to a stick.
 
The fuel level gage won't tell you anything useful about mileage, though many people think those tic marks are magically precise. You record from full fill-up to the next fill-up, the volume added based on the certified fuel pump meter. Also record the distance traveled. The car's odometer is also not magically precise, unless you calibrate it against mileposts on the interstate. Instead, use those mileage markers on a long trip or your phone's GPS data for miles travelled. I regularly got 22 mpg in my 1969 Dart with 225 slant. That was in the days before 10% ethanol in gasoline, which lowers mileage perhaps 5%.
 
Back in the day my first car was a 56 Dodge (54 american but updated) with 230 cu ins side valve six. It got about 8 or 9 mpg. My next car was a 1964 Valiant AP5 225 slant six manual. It had twice the power and was much better on fuel but the best I could get on a run was 15mpg. My next car was an ex police 1973 Valiiant Charger with 265 Hemi and four speed manual. Wow it was a rocket ship compared to the AP5 and would get an easy 26 plus mpg on a run.
 
In 1978 I bought my first \6 car. It was a 1970 Dart Custom with auto, power steering and 2.73 rear gears. I was the second owner. The best mileage it ever got has 17mpg.

My 1965 Dart with a tweaked engine, Clifford manifold, Edelbrock 500avs, Erson cam, dual dutras, 4 speed and 3.55 rear gears got 15mpg, if I stayed under 3500 rpms. At 3500 rpms, the secondaries would kick in and you could watch the needle drop on the gas gauge. But it ran mid 10's in the eighth.

All things are relative.
 
BillGrissom said:
The fuel level gage won't tell you anything useful about mileage, though many people think those tic marks are magically precise. You record from full fill-up to the next fill-up, the volume added based on the certified fuel pump meter. Also record the distance traveled. The car's odometer is also not magically precise, unless you calibrate it against mileposts on the interstate. Instead, use those mileage markers on a long trip or your phone's GPS data for miles travelled. I regularly got 22 mpg in my 1969 Dart with 225 slant. That was in the days before 10% ethanol in gasoline, which lowers mileage perhaps 5%.
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22 mpg at what speed ?
 
In Australia [ [post #47 ], before litres, we used Imperial gallons. Not sure if James is using Imperial, or converted to US gallons which are about 7/8 of an Imp gallon.
 
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