Nightpath Posted July 20, 2014 Report Share Posted July 20, 2014 This September I'm finally getting around to transplanting the 4.0l/aw4/231 into my Eagle (or 242 if anyone wants to swap maybe). Anyways, what are your thoughts on gearing the rear? I'd like to use a 3.07 set for hopefully a bit better mpg, but some people say that too low a gear causes it to not like OD. A happy medium would probably be 3.2x gears...but was there ever such a thing in jeeps? Stock for the XJ is 3.54 which is ok, but I found my old xj to be a huge pig (15 mpg all day long). The Eagle is about 100 pounds or so lighter than the xj, but the xj drivetrain is lighter so the engine will be pulling less overall. What are your thoughts on gearing? Link to comment Share on other sites More sharing options...
sar4x4 Posted July 20, 2014 Report Share Posted July 20, 2014 Tire size. An engine should run something like 2200 rpm on the highway, you can find more details on line. Typically work with 1:1 high gear, not overdrive, and your tire size, that determines your rear end ratio for highway driving. Link to comment Share on other sites More sharing options...
Nightpath Posted July 22, 2014 Author Report Share Posted July 22, 2014 I think that 3.21 would be the lowest/safest to use possibly, without ruining the rpms. Could be that 3.07 would work, but with a bit larger tires it may cause problems by keeping it in too low of a range. Link to comment Share on other sites More sharing options...
TomWood Posted July 22, 2014 Report Share Posted July 22, 2014 I ran a cherokee with 235/75/15 tires and 3.07 with a 4.0L and manual trans. It was beautiful on the highway and I think I averaged around 25mpg on a trip to moncton and back. Did not have to downshift on hills, and didnt push it. I was driving around 100km/h which is the other side of mileage. If you drive at 120 on the highway you may get 20mpg out of the 4.0L but it would be a struggle I am guessing. Link to comment Share on other sites More sharing options...
cman monster Posted July 22, 2014 Report Share Posted July 22, 2014 gears are in your eagle now , put the 4.0l motor and tranny in and see whats it like before you start swap gears and money and that wait you have a starting point and know what gears you need higher or lower in my jeep tj 2.5l when it was stock and had 4.10 I got 16 to 18 mpg and now with 4.88 gears and big tires and not stock I get 24 to 26 mpg it's all about what rpm your motor works best at and gear it for that Link to comment Share on other sites More sharing options...
Nightpath Posted July 22, 2014 Author Report Share Posted July 22, 2014 It has 2.73 but the rear axle is shot. Sounds like a chainsaw Link to comment Share on other sites More sharing options...
My04T4R Posted July 22, 2014 Report Share Posted July 22, 2014 Lol Link to comment Share on other sites More sharing options...
Eastcoastcam Posted July 23, 2014 Report Share Posted July 23, 2014 Did I read somewhere that you have a donor XJ? Get everything swapped over and start from there... No need to start spending more money until you see what it does. Link to comment Share on other sites More sharing options...
Nightpath Posted July 23, 2014 Author Report Share Posted July 23, 2014 The rear axle has no diff cover, so I was debating gearing it somewhere different. Theres a few 3.07 axles around I could get, but rather than blow the cash first to see how it works I'd rather see if anyone knew. Link to comment Share on other sites More sharing options...
Nightpath Posted August 12, 2014 Author Report Share Posted August 12, 2014 I've decided on sticking with the stock XJ parts (including rear axle with the 3.55 since i have the front to match for the Eagle). If I want to up MPG I can get a throttle body spacer, or an upgraded distributor for a hotter spark (which I might) If I want to adjust for RPM I'll just bump up a tire size or 2 (29" looks good, can fit 31" with some trimming)...make that beyotch look like a kids RC car! Link to comment Share on other sites More sharing options...
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