i'm looking at maybe getting a 77-79 4x4 tuck with a I6 300. what gears and trans and carb setup will give me the best mpg daily driver. not looking to put a lift or big tires or lots of pulling, have a 99 7.3L F250 for that. just looking to see what is the best setup for these tucks. as far as the speed limit most for the time around 55mph not a lot of hills but 2 small towns that have 3 lights. i know that they are not going to get 25mgp but just the best for stock trans gears.

thanks matt

also will going to a 250 vs 150 make a big mpg changer?

 

I have a 3.08 rear in mine with the 4sp od. I get about 19-21 hwy and 17 city.

 

Usually the best highway gas mileage comes from either a 2.73, 3.00, or a 3.50 (depending on the size of the tires) rear with an overdrive, (but I don't think the 77-79s had any overdrive options).

However, since you'd only be doing around 55mph, no overdrive won't be a problem.

Honestly, for your situation, speeds, slight hills, I'd say a 3.50 would be your best bet. It won't be winding out at 55, and it'll give that little lower end grunt that'll make it so the engine's not overworking to get you moving.

As for the carb, it only came with a 1bbl stock.

 

I would disagree with AB. I would drop down to the 331:1 rears. I often haul/tow with my truck, and freeway fly empty too, and they seem to be good all around gears.

I changed from 374's, and love the difference. Of course, I have oem tire size, with a C6 ... no OD, sorry to say. My engine is a bit modified, and I get 16 on the freeway, so you should get better than that.

 

Heh, in my defense, I'm used to the Broncos. The Broncos only came with 3.00, 3.50, or 4.11. Haven't memorized all the truck ones yet.

But yeah, since there's a gearset between a 3.00 and a 3.50, that'd be the best of both.

 

I'll disagree with both of you There are way too many variables to be able to say x:yy gearing is "best". The changing of gearing, in and of itself, has minimal impact on mpg and even at today's gas prices, the ROI from investing in a set of gears may be a long time in coming. Tune up, wheel alignment, tires at maximum rated pressure, but most of all the operator's manner of driving are major factors in whatever mpg one gets.

 

i'd say 3.55 or 3.73 and a zf 5. @Harte3 How can it just be how you drive. There is a big difference in rpm on the highway with 3.50 and 4.10's.

 

When someone asks such a question (what are the best gears for mpg, etc.), I automatically assume we are speaking of a scientific experiment, where we have a control vehicle, driven exactly the same by a robot. And we get the mpg from one gear set, and then try another under the exact same circumstances, course, etc.

But w/o that control or assumption, yes, there are a million variables upon which we could endlessly debate. But in a lab., the lower the ratio, the better the mpg.

 

The first problem is the "best" word. It is highly subjective and nearly indefinable. "Best" is going to be different for different drivers because of the infinite variables. For example; changing ratios from 3:0 to 4:10 might be "best" for some depending on their usage of the vehicle and other variables but there is no single ratio that can be said to be "best". There are by far to many variables. Given the fixed ratio of any given vehicle and given this vehicle is in proper operating condition, the manner of driving IS the major contributor to mpg or the lack of it.

 

i guess i should have been more clear i dont intend to re-gear or new trans just looking for the best stock setup. sorry should have said that at first.

 

That's how I took it. If you're going to search out a truck, which one are you going to aim for.

Sure, a person can learn how to get the best mpg out of any gearing, but some are going to be easier than others. Some gears are known for mpg, some are known for grunt. If they weren't, there'd only be one gear set and only one transmission.

 

thanks for the responses i will see if i can 100% make up my mind

 

A truck running 3.31s with a c6 would be about comparable to a manual running 3.55. The torque converter multiplies torque when you start off so you don't lose grunt with slightly higher gears. Also the torque converter doesn't have a clutch so the transmission input never spins faster than 85% of the engine speed. So a manual can use slightly lower gears and still spin the motor at the same speed for a given cruise MPH, no 15% slippage with a manual.

I agree with Harte3 that it's mostly about keeping the engine tuned up and running tire pressure near the maximum, keeping the truck aligned, and accelerating moderately.

If you drive mostly city look for gearing in the mid 3s. If you cruise mostly highway, look for gearing in the low 3s

 

No transmission Q's?
None for the carberation?

Matt - how bout if U let us know what tires you've picked.
(sounds like a "DD around town" rather than a hwy truck or a work truck).