The U.S. Government used to hold mileage competitions that the car companies would compete in. Chrysler was a regular winner at this event. This is worth looking up.
Real world MPG story from yours truly. Let’s start the story with the car and drive train. I have a 1979 Dodge Magnum with a 8-1/4 rear end, housing 2.76 gears that turned 235/60/15’s. The transmission is a dead stock 904 of the same year. IDK if it was a lock up or not. These parts are stock to the car and remain so. Initial mileage was normally 9-10 on the Hwy with the leanbun.
Horrible! This can not due!
The engine is also stock to the car. It is a 360-2bbl. When I first revived the parts car that sat in the back weeds of a body shop, it was still running the leanburn ignition system. Knowing there horrible reputation, it was removed and replaced with a MP Orange box and ballast. A junkyard distributor was used and the only description from them was, “It came out of a truck.” Lord knows the curve within. It was never changed.
I’ll skip ahead to the parts change out list;
Chrysler Orange ignition & ballast, JY distributor
‘72 Trap door air cleaner w/a K&N filter
Carter Competition 600 AFB
Factory iron TQ intake, egr disconnected which renders it closed off and non effective or contaminating to the engines air fuel charge.
Duel exhaust custom bent off the exhaust manifolds @ 2-1/4 inches. Due to the then state law, it was a MUST HAVE catalytic converter or fail emissions, period!
The exhaust was give. An “H” pipe before the twin high flow cats that I believe were Magnaflows.
(Sorry, it’s been a long time.)
Thrush Turbo mufflers we’re used. Exhaust went to the bumper.
After some tuning, in which a lot of fake testing was done and a bunch of spark plugs were used, mileage rose to 17-18 on the Hwy. not to bad but I did want to try for a little more. More the merry right?
While I personally have had a lot of bad luck with MSD ignitions, this is the one and only box that has performed as it should. The MSD 6A box delivers (as you all know) multiple sparks below 3,000 rpm. Since the car lives under this at cruise, the result was another 2-3 MPG’s.
There seemed to be a minor 1 mpg variance that I have come to the conclusion of the quality of fuel. Routinely it was mail a solid 19. When I realized that all fuels are not the same, I paid attention to what gas station gave the best results. It was the busiest gas stations since there consistently getting fresh fuel. Not one brand over another although I am sure there is a better fuel at a name brand station over another name brand station.
Best fuel was purchased on the N.J. Turnpike. On a constant cruise on my road trips in and out of Richmond Va. & Northern Ga., the absolute best was 21 mpg’s.
Is 21 mpg’s good? Is it great? Is it what one should expect?
IDK! But it sure beat the heck out of 9 or 10 on the Hwy.!
Considering the car was fully loaded minus a T top or sunroof option or the tow package, the car weighed in over 4,000 when I’d travel with the wife & kid. A packed car, not an over loaded car did IMO, pretty good.
Could I have obtained more mileage? I think so. I’d start with the list below! Yes! It starts with no cats on the exhaust! LMAO! Starting from top to bottom on the engine.
Cold air induction. A fresh air tube on the air cleaner was initially used, but it’s age was long over due and discontinued in its use.
A TQ carb may have helped. As well as an aluminum intake like a Edelbrock Performer.
Headers! But I don’t think a bigger exhaust pipe would really show an gains since the engine is a low powered smogger.
A mileage cam to replace the factory cam, even though the factory cam was a broom stick. Rearranging the cams timing events can net gains.
A better distributor curve.
A MP viscous fan.
Taller tires reduce cruising rpm, great for the interstate travels, but hurt around town mileage. The stop and go as well as NYC rush hour traffic can be ruthless on any mileage attempts on any car.
The only tip I can give while you, yourself might attempt in mileage gains would be to not only use a multi strike ignition system, but to experiment with the spark plug gaps. Also, run the carb as lean as you can and practical. To lean drives engine temperatures up, cause misfires, kill power and make rod a crappy experience.
Happy mileage hunting!
