I have a 2002 F-150 Supercab with 5.4L 3:55 auto 2wd with Limited slip. I cant get anything better than 18mpg on the freeway, and I was wondering if there is anything I can do to increase mpg but not hinder performance. The truck is still completely stock. Would going to a 3:73 improve anything? I also only have the std 235/70-16 BFG that came on it... looking for advice. Thanks

 

for mpg improvements i'd stick to the basic intake/exhaust mods first. 3.73's might decrease your gas mileage since youre going to be running higher rpm's at cruising speeds.

 

You could do 3:31's or 3:08's? It will be a complete dog off the line and down low for pulling/performance, though. I actually think you're doing pretty good at 18mpg on the freeway, for a 5.4 anyway? If you go lower on the ratio, your rpms will be higher=worse mpg. I could be wrong though,,,,98

 

The higher the rpms doesn't neccessarially mean lower mpg. Raising the rpms slightly might put the truck more into the powerband. It depends on the engine. I'd say that going from a 3.55 to 3.73 is going to be barely noticable. Best way to get what you want is through intake, chips, etc. Also the fact that a new gearset with install is going to run you about $300 to $400 for a 2wd. This to me is definetly not worth the added cost and hassle.

 

18 on the highway, and you're not happy with that? The best I've ever gotten was 17 and that was a straight 300 mile run down I5 on the "Grapevine" in Calif.

I average 14-15 on a daily basis. Be happy with 18. It's a #5000 brick, so it ain't gonna win any EPA awards. That's what Honda's are for!! Ha, Ha

Some lower gears might help in the city? They help you get moving easier, so less gas is actually needed. I wouldn't do to much to it however, if mpg is still your goal. Improving performance usually has the cost of using more gas. Not so much from the mod, but the fact you can't keep your foot out of the gas because you're having so much fun!

Let your motor 'break in' some more, and you'll probably see it improve some too. It's probably still pretty 'tight'.....