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37" tires + auto= Lower gears or just not enough power??

XJ McLovin

NAXJA Forum User
Location
Las Vegas
Ive got a 99 XJ with 37's, 5" of lift, 4.88's and an auto trans. Engines in very good condition, all tune ups have been done between engine and trans since Feb. when I bought it. Truck drives great on the street, highway, and its a badass on the trail.

Only problem is no power on the steep highway inclines. It feels like its a dog in 3rd when i hit a certain grade. Ill have it floored and Im bearly holding 65 in 3rd and there are times it feels like it needs to shift into 2nd and scream at nearly 4500-5000rpm.

Im taking a trip from Vegas to Moab in two weeks and Im wondering if 5.29 (weird currie ratio for 9" HP) is the fix or if I just have to come to terms with the fact Im trying to force a brick through the wind on 37's with around 200hp at the crank.

What do you guys think, should I spring for the gears?
 
I don't think you'll find much relief for steep grades no matter the gearing, underpowered is still underpowered. If your happy with the offroad performance, I'd stick with the 4.88's. I'd try the basic power adders like cold air intake, exhaust, and a programmer for the money you would spend on regearing. 20hp doesn't sound like much, but its 10% for our poor little 4.0's.
 
It actually has an intake, headers, exhaust, bbk throttle body, and power distributor ignition that came with the truck when I bought it. The only lower gear choice for the axles are 5.29's. I know a lot of TJs move up to 5.13 or 5.38 with an auto and 37's but they also don't weigh the same as an XJ. I know a v8 swap is in the future but not till next year, just can't decide if these 5.29 gears are going to help the drive ability in the hills or if they are going to be a waste.
 
it's going to be a dog with 37's, period. mine is, however if i flog it i can hold decent speeds on the climbs (manual trans). gears definitely help, i run 5.38's. it revs high, about 3100rpm's at 80mph
 
For me its going to be 5.38's and 37's. gearing as low as I can. Then I will also do some of the power add ons a little later. I remember a article, think it was JP magazine. But they did a comparison between gears and your typical pawer add on's. The gears proved to be a better bang for the buck.
 
5.29 is really not THAT much of a difference of 5.38. The larger/more rolling mass with 37's is going to affect driveability regardless.
 
gear as deep as you can. but nothing is going to make a 4.0 turn 37"s like it turned 29"s
 
I had 5.13s and a stroker with 37s, drivability was nice but I'm sure it would have sucked with just a 4.0

gear as deep as you can IMHO
 
the 5.29s will help , and it sounds like other than building a stroker , or going v8, theres not a lot you can do. mine dogs in the mountains too on the 36s and heavy headlocks and 4.88s. I am planning on a 4.5 stroker eventually, and whenever I go bigger on axles ill go to 5.38s or deeper, but all of that might be years away. ive just been dealing with it for years . Something to consider would be to get a cheap set of 33" a/ts for long drives if you truly don't need the 37s for that specific run. or tow the 37s on a trailer. Ive been considering getting a cheap set of 33s for the easier trails just to save on power and probably MPG.
 
Thanks for the advice so far. Ive done the research I just needed to hear some opinions before I fell into one of my 2am internet shopping sprees.

Im tempted to do the gear swap this week but just not sure its going to be worth it. The cost would be roughly $650-$700 for gears and install kits with me doing the labor. Im going to Moab on the 18th for a week and there are some pretty steep inclines on the drive from Vegas.

A V8 swap seems like the only answer and was on my bucket list before I bought the XJ. Actually one of the reasons I choose the XJ was how it easy it seemed (aftermarket support) to put a newer chevy v8 in one of these. Ive budgeted about $6000 for that project and it will probably take until next year. No need for 5.29's with 300+hp, either.
 
Gears will help.

A stroker (or V8) would help a lot more. I run on 5.13's and 37's, I don't even downshift to third driving from OC out to vegas.
 
lol. i drove to the trail in that config for 3 years before i bought a trailer.
 
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