Slant Six mpg's?

[/6 Matt]

I get 15-22 mpg around the city and 25-27 mpg highway. 5W-30 castrol motor oil and a 2.76 rear end with gear problems and bad bearings up the ying-yang (gonna get an 8-1/4" soon anyways), oh yeah, the tranny is getting tired too...

177K miles or maybe 277K miles hell it could even be 377K miles, some 40K miles on the engine. Original transmission and rear though...

 

[fourspeed]

I would gladly take some of your guys mileage.
Im only getting 7 mpg in town. Thats without idleing any. Easy on pedal to. Just replaced distributor cap and plugs. New air filter and fuel filter. I dont know whats wrong with it.
its a 73 swinger with 225 slant 6 automatic. All stock.

Better check for holes in your gas tank.

I had a '67 Dodge Cornet 4 door with a slant auto, all stock except I swapped to electronic ignition. Best ever was 22 MPG all highway driving. Not bad for a big old square box.

 

[73_Dart]

Better check for holes in your gas tank.

I had a '67 Dodge Cornet 4 door with a slant auto, all stock except I swapped to electronic ignition. Best ever was 22 MPG all highway driving. Not bad for a big old square box.

I have looked, And i cant find any leaks anywhere.

 

[trapster]

the old gas tanks are not very airtight so you will get some evaporation .
and you may need to replace the filler tube gasket it has been known to cause leaking problems if you fill your tank more than 3/4.

good luck

 

[2 Darts]

I hear the 2 reasons the slant 6 went by the way side,emissions and not able to meet government mpg standards.

My guess is it was dropped due to cost considerations. The 3.9 V-6 can be produced with the same tooling as the 318 V-8. It uses the same transmission and exhaust pipes (in the Dakota) as the V-8. The accessory equipment for the V-6 are the same as the V8, too.

As for emissions, Mopar could have tweaked the head and installed Sequential Multi-port Fuel Injection and solved those problems if the engine really had a future for the company.

The Feather Duster and Dart Lite in particular exceed the CAFE requirement and wouldn't need offsetting sales of little FWD cars shaped like cough drops.

FWIW: I'm getting about 14-15 mpg in town and 22-25 mpg highway depending on speed and temperature. The car is a 73 Dart Custom, 2.93:1, 904, 205/60-15 tires. Only significant mod to car that would affect mileage has been the installation of an oversize exhaust manifold with no carb heat, and a 2¼ exhaust.

 

[ESP47]

My guess is it was dropped due to cost considerations. The 3.9 V-6 can be produced with the same tooling as the 318 V-8. It uses the same transmission and exhaust pipes (in the Dakota) as the V-8. The accessory equipment for the V-6 are the same as the V8, too.

As for emissions, Mopar could have tweaked the head and installed Sequential Multi-port Fuel Injection and solved those problems if the engine really had a future for the company.

The Feather Duster and Dart Lite in particular exceed the CAFE requirement and wouldn't need offsetting sales of little FWD cars shaped like cough drops.

FWIW: I'm getting about 14-15 mpg in town and 22-25 mpg highway depending on speed and temperature. The car is a 73 Dart Custom, 2.93:1, 904, 205/60-15 tires. Only significant mod to car that would affect mileage has been the installation of an oversize exhaust manifold with no carb heat, and a 2¼ exhaust.

That's strange that you have such a big difference in city and highway driving. Especially with your 2.93 gear. You'd think you'd be pulling better mpg's around town with it geared a little better than most stock 6's. Maybe it has something to do with you using extra gas when its cold due to no carb heat.

I have 2.76 gears and pull about 19-20 if it's city only driving. I just did a relatively flat run with 75% of my tank going towards a highway run where I did 75-80mph the whole way. The other 25% was city driving. Got 21.8 mpg out of that run. A little better than I thought with how fast I was going. For some reason I seem to get just about the same mileage whether I'm in town, highway, or doing 60 or 80.

 

[Backtobasics]

Bear in mind that the Dart Lite and Feather Duster numbers were on the old MPG estimate systems. No accessories, and largely estimates by the manufacturer.

I am not aware of any slant 6ers who are legitimately getting 30+ mpg. If they are out there, I have not seen them advertising their successes. I especially don't see it with todays craptastic fuel with ethanol blends, etc. I have seen sporadic posts from people from time to time with the claims, but in almost all cases, it was a random highway jaunt, with no before or after testing to confirm. Bear in mind that even the length of the fuel filler tube makes a difference, as I have read that the DLite and FDuster models had a tube that did not allow full filling of the tank, presumably to carry less fuel and less weight? It would not be very hard at all to have what appears to be a killer MPG run, simply because the angle of the ground at the gas station caused the the pump to kick off early and short fill the tank by a gallon or ?
I would love to see one posting those numbers, but I get the feeling it would have to be a dynamically tuned and built combination, targetted specifically towards highway MPG, using all kinds of tips and tricks to get there. It would probably be a snail around town due to gearing, etc.

 

[Backtobasics]

FWIW, my Dart Lite got a consistent 18 with a combination 25/75 combination of in town / and highway, and the highway runs were 55-65 in the AM, minimal traffic, and 25-30 average in the PM in "stop and go" traffic. Combo is 3 speed with 2.94 gears on modern radial tires, and junk carb, overall. 55mph was happy, but keeping with traffic had me at 65 which turned more RPM then I liked. With the OD trans, better carb, and mpg inspired tweaks (belly pan from bumper to K member, HEI mod, fresh tune up, index plugs, synthetic fluid in trans and diff) I am shooting for 25 combined.