Fuel economy (odd ball)

[Dan201]

What is the difference in mpg in a slant 6 4 speed pickup compared to a 4 speed volare or an automatic dart? I am driving my 74 sedan about 80 miles a day back and forth to work and was wondering what I might save going to a 4 speed with overdrive

 

[66aCUDA]

Dan
A lot depends on the transmission. Some of the trucks got the NP 4 speeds with a granny first gear. No savings there. The 833OD's were good and may save you some fuel in a car. As for your Auto equipped Dart Lets see where your at tune wise and maybe we can increase your mileage enough that you wont have to go thru a trans change.
Shoot us where your at and lets see if we can help you improve your mileage.
Frank

 

[mikeys toy]

I put a van 833OD in my '69 Belvedere wagon 225 super six, 323 gears and was getting 22-25mpgs @ 65mph.
I get about 11mpg in my '75 D100 225, Holley 1bbl, NP435, 3.55 gears.

 

[Dan201]

Right now my car is getting about 7 kilometers a litre but the valves need adjusting (hopefully saturday) the rear most likely is getting worn out, and the engine doesn't run perfectly smooth (most likely uneven compression on the cylinders) good car over all though especially right now driving in the winter the suregrip comes in handy. It needs fuel lines as well but I really don't have anywhere to work on it and I don't like crawling in the snow to do fuel lines. I changed the heads to a newer one with small spark plugs and no druel tubes don't know if that matters it seems a little smaller but I had 2 bad valves on the old head.

 

[66aCUDA]

Do a valve adjustment. Dont forget the intake and exhaust swap at the 3-4 junction. I would not think the difference in Cyl pressure would make it stumble. Check the carb it may be time to rebuild it. DO NOT buy a rebuilt carb have someone rebuild it OR at least keep you old one so you have a backup. Maybe install and extra fuel filter to get you through the winter.
Good Luck,
Frank

 

[mpgFanatic]

What is the difference in mpg in a slant 6 4 speed pickup compared to a 4 speed volare or an automatic dart?

That's an apples and oranges comparison, because wind resistance is your biggest highway contributor to fuel consumption. Choosing a truck instead of a sedan doesn't seem likely to help you.

I am driving my 74 sedan about 80 miles a day back and forth to work and was wondering what I might save going to a 4 speed with overdrive

Need a bit more information. An overdrive gear will almost certainly save money, as long as the engine still makes enough torque at whatever is the reduced rpm. But it's going to change how you drive in the city. Sometimes an overzealous choice of "highway gearing" actually hurts city mileage because the engine ends up working too hard at those lower rpms.

Right now my car is getting about 7 kilometers a litre but the valves need adjusting (hopefully saturday) the rear most likely is getting worn out, and the engine doesn't run perfectly smooth

Um, it seems like you've got a whole lot of things you could do that are a whole lot easier than changing a transmission! Valve adjustment, timing check, making sure the vacuum advance canister is still working...

Let's see, 7km/l = 16.5mpg. This is in an automatic 74 Dart in a snowy winter climate? Might not be all that far off. Depending on the rear end ratio, I wouldn't expect more than about 19-20 mpg (8km/l) anyway, for those weather conditions.

Here's how difficult it is to predict gas mileage based on how smoothly you think the engine is or isn't running: I once tuned up a 170 slant six in a little 1965 Valiant to the best of my then-inexperienced ability, got my highway mpg all the way from 14 to 16. Frustrated. Everything seemed to be running just fine, it purred like a kitten, but drank fuel. Rebuilt the carb. Still purred like a kitten, highway mpg jumped to 27. Learned a lot, that day.

- Erik

64 Valiant, 170 3-spd
82 Volvo wagon, 5.0 5-spd