91' F150 5.0 4x4 5spd manual with 3.08.. 31x10.5 tires

I'm wondering if going with a 3.73 to save the 60 bucks for a new diff shell/housing for the D44 TTB will really be worth not going with the 4.10 as far as fuel milage goes. And if there's really that big of a difference in trq/pwr on these two gear ratios, for that's a big part of my decision as well. If the trq/pwr in the 4.10s is that much better than the 3.73 then mpg won't matter so much anymore. Just want some opinions here.

 

How about just some personal preferences for certain applications

 

Have you checked you mileage in 4th gear? vs. 5th
Does your transfer case have low range? Or do you pull heavy loads off road and fear you'll blow the 3.08? To be honest that 3.08 is going to be worth It's weight in gold as gas continues into price rationing long term.

 

No i haven't checked the difference between 4th and 5th. 5th is so gutless i only use it on very flat land, which is very limited near my home. 4th isn't much better, probably around 500 rpm diff at 60mph~4vs5. i can't shift into 4th until i'm going 60 in 3rd while driving uphill.
Yes i got 4L. Got a wood stove so i pull full loads in the back from time to time. And it's a truck, if i didn't want/need to haul things i'd buy a car. Once i beef up the engine a bit i may not have as many complaints about the 3.08, but i'm still not sure if it'll allow me to accelerate in 5th on small grades.
And if it's small differences in gas milage, i'm a single guy with my rig as practically my only bill. So i can dish out a lil extra dough.

 

Oh and as for selling or trading, this gear swap won't be happening till march. Still got some time left over here in the worlds biggest sandbox.

 

that's cool. sounds like you got a gear for just about any situation. I run in 3rd all day if that's what works, a truck trans. should do that I would think. full syn oil wouldn't hurt i guess. the old ones would run all day in any gear. I am not positive about these aluminum ones.
Has any one out there ever worn out 3rd in one of these new ones?

 

I would go with the 3.73 just because it is a good in between gear. Your gas mileage will go down but probably not as much as you might think. With a 3.08 gear your truck probably doesn't get up and go all that great, so most people who don't grandpa their ride will keep it to the floor to get up speed and keep it there. With a deeper gear you won't have to do that to get going. And as a bonus you should be able to cruise around in 4th gear, in town, and that will help with gas mileage some.

 

> Got a wood stove so i pull full loads in the back from time to time

Get the 4.10 gears. With the manual you can always get it into a higher gear where it doesn't lug. A lower rear end will save wear and tear on the whole drive train and your mileage might actually go up on the highway.

The trouble is you do not have the HP or tq with the 302 to move the truck properly and keep it in it proper powerband. Especially with tires two inches bigger then stock.

Plus, as you already noted, GA is hilly. You need the lower gears, especially with anything in tow or loaded down.

http://www.4lo.com/calc/geartable.htm

FWIW: We actually got snow in Atlanta last night and ice is still on my back porch!

 

That chart looks like an exellent tool, just one question have you used it yourself and been happy with it. Or if you haven't used it for a change does it at least match up with what you already got.

 

Metric engine, 4.56s for sure! Ford lost all bottom end in the 80s, keep it above 2100 at all costs, 2500-4000 RPM can be worth as much as 20% in fuel economy, and 30-70% more TQ. I swaped in a 5.0L for a tired 302, and milage went DOWN 15%, we had to drop gears from 3.73s to 4.10s. Whats bad, this truck never had more of a load than 3 adults and 7 bags of trash.

What part of Ga? In Dawsonville, I almost never use OD. The last time I did, 76 f100 302/SMOD/5.13s in a 9in gear w/38x13.50x15s.

Had a 95 Ranger 3.0L, couldn't even use OD w/3.73s @ 70.

 

Usually the RPM's up to the torque peak are the most efficient from the engine's stand point. Hp per gallon or whatever. But that's assuming that you can use a good bit of the torque for the job your doin'. The injected engines have fuel enrichment, and accelerator pump programed in just like the carb'd engines so if your're geared so high that you have to get into fuel enrichment, she goin'na suck gas. The increase in torque for that last 20% of throttle is way past the point of diminishin' returns. It definitely will help keepin' your total gear ratio lower. However you do it, by shiftin' down or lower rear gears. i miss the 6 to 1 low that the old 4spds had. i got a 91F250 302 5 spd 3.55 and my biggest gripe is low gear is to high. Once i get rollin', i can always find a gear to run in. i'm use to drivin' big old truck with small engines. The car only has 50 hp, so shiftin' on hills is natural. It tickles me to hear you young'uns got to go up the hills in high gear. 40lbs. per hp is about right for the street. On the track too much hp is just enough.