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Slow and Non-fuel Efficient XJ

X

xDARKWAVEx

NAXJA Forum User
Location
New Jersey
Hey guys, im new to the forum and this is my first question/problem I have with my XJ. Its a 2000 silver 4x4 classic and has treated me very well since I bought it. I raised it 4 inches, still has 31's on it, K&N intake and a magna-flow exhaust. It seemed after I raised it that it was much slower, like I had to press down a lot more on the gas pedal to make it go like before. Everyone I talked to said that it shouldn't feel like that and its prob just the feel of a raised Jeep. I installed a transfer case drop kit because I thought that by raising my jeep, I off set the axle and maybe thats why it was slower, but nothing. I also found a yoke-slip eliminator that the rubicon wranglers have, but those are real expensive, and would that even help? Also, I keep up with all maintainance and keep clean filters, but have horrible gas mileage, about 230-250 miles per full tank ! Anything you guys think would help ! Thanks
 
Yeah a SYE would help a little I'm sure. The main thing I am betting thats killing your mileage is stock gearing with 31's. I am in the same boat and while its not terrible on the interstate the mileage is Terrible in town.
 
Take out the TC drop, replace your motor mounts (and maybe tranny mount too) and install a SYE. Regear as FlexdXJ said - that will be most noticable. Also, don't forget to correct your speedo gear - you're probably getting better mileage than you think, because your speedometer/odometer are off.
 
X2 on the mileage inaccuracy, remember that the speedo is calibrated for ~27.6 inch tires... you have 31s on it that are probably more like 30.4. That means when your Jeep thinks it's gone 1 mile it has actually gone 1.10 miles, so multiply your current gas mileage by 1.10 and you'll get a more accurate figure.

As for acceleration, going to 4.10:1 gearing or even 4.56:1 gearing will help you there... you decide if it's worth 500 dollars in gears and parts and 500+ in install costs though.
 
JNickel101 said:
Take out the TC drop, replace your motor mounts (and maybe tranny mount too) and install a SYE. Regear as FlexdXJ said - that will be most noticable. Also, don't forget to correct your speedo gear - you're probably getting better mileage than you think, because your speedometer/odometer are off.
Click to expand...


I believe the odometer would be 16% lower than your actual mileage.

Lets see 27(approximate OEM tire size)/31(approx.)=.87097. Ok that looks to be about 13%. So the 230-250 you are seeing is actually 259.9-282.5 Miles per tank.
 
Last edited:
XJ's are slow and not fuel efficient to begin with :D

The t-case drop will not have an effect on your mileage.

The bigger tires will.
 
IslanderOffRoad said:
XJ's are slow and not fuel efficient to begin with :D
Click to expand...
I dunno what' you're talking about. I did 120 in my XJ once, back when it was stock... GPS verified. Was pretty scarily smooth and I didn't need a trip to jail so I only did it once. Statute of limitations has since run out :eyes: :D

As for not fuel efficient... well, yeah. Especially when not being slow.
 
If you want a "fast" or "much quicker" XJ, then you are probably in for an engine swap and some gears. Otherwise, as said, gears!
 
FlexdXJ said:
I believe the odometer would be 16% lower than your actual mileage.

Lets see 27(approximate OEM tire size)/31(approx.)=.87097. Ok that looks to be about 13%. So the 230-250 you are seeing is actually 259.9-282.5 Miles per tank.
Click to expand...


I don't follow your calculation. Don't you want the percent change in tire size which would be 31-27/27?
 
i am running 3.55 gearing on 33's getting 4.56 right now as we speak but i have only gone 170 miles and i have not replaced the speedo so really how far have i really gone?
 
Divide by the old rolling height (for better accuracy than diameter) then multiply by new rolling height, that's your real mileage assuming the odometer was accurate before. Rolling height is the distance from the ground (use a flat level surface for measuring this obviously) to the center of the rear wheel hubs.
 
well, idk what the old rolling height was cuz i dont have the stock tires anymore so can somebody help me out and do the math if they know the stock rolling height?
 
kdub41 said:
well, idk what the old rolling height was cuz i dont have the stock tires anymore so can somebody help me out and do the math if they know the stock rolling height?
Click to expand...

There are tons of calculators online for this.
 
89xj said:
when my 89 xj with a 5-speed was stock, i felt it was fairly fast. i dont consider 18mpg average for an suv to be "not fuel efficent".

adding larger tires without regearing is most peoples problem.:rattle:
Click to expand...

Mine felt decently quick when stock too, but if I really wanted to go fast, I wouldn't be driving an XJ.
 
ok so here is what i found but is a 280/75-15= to a 33 in tire?

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference

225/75-15 6.6in 14.1in 28.3in 88.9in 713 0.0%
280/85-15 9.4in 16.9in 33.7in 106.0in 598 19.3%


now what do i do to figure out how many mile i have really gone? cuz my speedo says i have gone 150 but with this difference what would it really be?
 
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Khary23 said:
I don't follow your calculation. Don't you want the percent change in tire size which would be 31-27/27?
Click to expand...


OK so 14.6%, I was off 1.6%, Sue me! :rolleyes:







:D
 
kdub41 said:
ok so here is what i found but is a 280/75-15= to a 33 in tire?

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
225/75-15 6.6in 14.1in 28.3in 88.9in 713 0.0%
280/85-15 9.4in 16.9in 33.7in 106.0in 598 19.3%


now what do i do to figure out how many mile i have really gone? cuz my speedo says i have gone 150 but with this difference what would it really be?
Click to expand...

the difference between stock and 33' is about a 20%

so 150 miles would be 180.

20% of 150 is 30, so 150 plus 30 equals 180.

wow
 
kdub41 said:
ok so here is what i found but is a 280/75-15= to a 33 in tire?

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference

225/75-15 6.6in 14.1in 28.3in 88.9in 713 0.0%
280/85-15 9.4in 16.9in 33.7in 106.0in 598 19.3%


now what do i do to figure out how many mile i have really gone? cuz my speedo says i have gone 150 but with this difference what would it really be?
Click to expand...


You aren't real quick are ya? My math was a little off but if you would have read my post it would have roughly been correct! :doh:
 
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