Hey guys,

I have a quick question regarding axle ratios and mpgs.

I've done quite a few things to lower the gas consumption of my '91 XJ Limited, including replacing an O2 sensor (upstream), TPS, new K&N intake, and an aftermarket exhaust (not the greatest though), plugs and wires, etc.. Afterwall, it's my baby, and also my daily commuter. Thing is, I'm only an E-4 in the US Navy and gas is expensive. I'm averaging 12.5mpg at BEST, and my commute is around 24.5 miles each way.

I don't expect to get 30mpg outta my XJ, or even 25. I know that XJ = brick when it comes to aerodynamics. But, after a lot of reading I was thinking I could possibly do an axle swap to a different ratio to help me get better torque at highway speeds and therefore better mpg. And it could also help me get better response from the throttle when I'm at highway speeds.

Right now I've got whatever ratio came stock with my XJ. I'm gonna guess it's 3.73:1 due to the fact that it's an inline 6, 4.0L, auto, and has a tow package (http://en.wikipedia.org/wiki/Jeep_Ch...le_Gear_Ratios).

My question is, what ratio would you guys recommend if I'm on a 2" lift and on 30x9.5 BFG A/Ts and where could I acquire said parts (online, etc)? There's a couple great junkyards nearby if nothing online is cheap and I would be more than happy to go out and mess with 'em in the sake of mpgs.

PS: I'd bet a lot of ppl will recommend upgraded injectors for better MPG. Just ordered em tonight -- they'll be installed next weekend.

Thanks!

 

If you need different gear ratios you don't have to swap axles. Simply buy the gears, install kit & have the work done by someone who knows what he's doing. Also, you didn't say if it's auto or manual. If it's auto your gear ratio is 3.55. I can't say for manual.

 

manual would most likely be 3.07s....that 3.73 gear package was pretty rare. i have a 93 cherokee country with the tow package and it had 3.55's(and 10 of my other xjs!) steepest gear set i would run with 30'' tires would be a 4.10. you could do a 4.56, but i think that would hurt your mpg at highway speeds.

if you are all-good with junk yard parts, just go grab some 4.10's out of a 4-cyl cherokee.....most had 4.10's.

 

I understand your frustration with mediocre fuel economy, but you need to crunch the numbers before you spend a bunch of money on gears. If you're burning 4 gals of gas a day, how long will it take to pay for the gears if for instance you get it down to say, 3.5 gals./day?

I think you can buy a lot of gas before you come out ahead. You might be better off looking at a smaller car or even a motorcycle for a short Florida commute.