better fuel mileage

[cajun chevy]

Hello out there
I have in my 1972 c10 307 v8, 4 speed, think it's a sm465, 373 gears in rear , 245/60 r 15 front tires, 275/60r15 back.
My question is what would be cheaper for better gas mileage. Changing the transmission or rear end gears. Thanks.

[Swar]

4 speed manual? You might see a difference in mpg if you put in a 5 or 6 speed. Not so much with changing the rear because it doesn't have overdrive. Taller tires might help on the highway.

[cajun chevy]

I would like to keep the tire size I have, what trans would be good, I don't plan on hard takeoffs.

[67 chevelle]

rear gears would be cheaper 3.42s would work

[Swar]

Gears would be cheaper, but I don't think you'd see a big enough improvement to justify it.
Save up for a decent 5 speed. It's more money and more work, but that's what I'd do. 3.73s are a good ratio for a setup like that. A Tremec 5 speed would be a really nice mod for something you want to cruise down the highway in.

[leftybass209]

Gears are cheaper but to do it properly isn't cheap in and of itself. When a truck is far off the mark of stellar fuel mileage as ours are (no offense) there is little you can do to improve your fuel mileage to warrant the initial cost. It's going to be in the thousands to save 10 bucks per tank. Then, you'd have to hope your engine survived long enough without a rebuild to start pocketing the fuel savings.

[cdowns]

Get a geo for better mileage if thar's what u need

[67ChevyRedneck]

Swapping the entire rear end for a 3.08 rear would likely be the cheapest. I've seen them range from $100-250. Compared to a 3.73 that's a 17% reduction in gearing (but don't expect to see a 17% fuel savings!) You might get a mile or two per gallon better.

OD is the best of both worlds. You can keep your 3.73 for grunt but get a ~30% reduction in OD.

[tranz am]

the ultimate transmission and rear end combination for mpg's has got to be a t56 and 3.73's.

[cajun chevy]

Thanks guys, gas here is 5 bucks a gallon, everything helps.