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Old December 30th, 2012, 08:34 AM   #1
project98
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98 TJ performance increase

I have a 98 TJ with the 4.0 L, which I'm wanting to squeeze better performance out without swapping motors. My thoughts are to port and polish the head and possibly the intake manifold. I'm also wondering if there are performance chips out there that anyone would suggest. I don't have the budget for turbo charging, and just want to know if I can do a few tweaks to get better performance and maybe increase in mpg over the road.
Any thoughts?
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Old December 30th, 2012, 08:38 AM   #2
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Regear the axles.
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Old December 30th, 2012, 08:39 AM   #3
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I forgot to mention. I did a 4 inch suspension lift with 1 1/2" body lift. So far I have headers, but I just getting ready to go through the engine. I will probably upgrade the axles later too.
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Old December 30th, 2012, 08:40 AM   #4
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Re-gear the stock axles to what? I'm not savy on gear ratios.
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Old December 30th, 2012, 08:42 AM   #5
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It all depends on tire size. But you will get better gains from that than sticking money in that motor. IMO.
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Old December 30th, 2012, 08:45 AM   #6
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Right now it has some worn 33's and I would like to run that size if the stock axles will handle it. Probably just go duning until I get better axles with lockers. I'll be buying new tires before I put it on the road.
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Old December 30th, 2012, 08:58 AM   #7
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When I got this jeep the tranny and transfer case were toast. I picked up another transfer case and installed a slip yoke eliminater kit in it. I just picked up another tranny yesterday for $65 and will rebuild it. Then I'll be srambling to get it running and on the road ASAP.
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Old December 30th, 2012, 09:05 AM   #8
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Quote:
Originally Posted by curbdog17 View Post
It all depends on tire size. But you will get better gains from that than sticking money in that motor. IMO.
Re-gear for sure. The minimal gains on that motor aren't worth the pennies.
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Old December 30th, 2012, 09:06 AM   #9
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I'd recommend 4.56 gears if you're running 33s. May want to consider finding an 8.8 rear axle to swap in before you dump the money into regearing. Not a bad swap if you have basic fab skills.
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Old December 30th, 2012, 09:07 AM   #10
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Where do I learn about gear ratios to best use?
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Old December 30th, 2012, 09:09 AM   #11
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Try here.

www.4lo.com/4LoCalc.htm
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Old December 30th, 2012, 09:13 AM   #12
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Are the 8.8 axles relatively easy to come by and adapt to the tj? What about dana 44's? What's the thoughts on that?
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Old December 30th, 2012, 09:14 AM   #13
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Thanks for the link robbietap.
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Old December 30th, 2012, 09:18 AM   #14
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Tie yourself to your chair and search your question. Should hear back sometime tomorrow, these are questions that you can read about for hours and spend huge $/time or spend little $/time depending on your ability. Good luck.
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Old December 30th, 2012, 09:22 AM   #15
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I have been reading and thought I would inquire here to get tried and true results and opinions from you guys. I appreciate feedback as I am learning.
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Old December 30th, 2012, 09:28 AM   #16
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There are few low dollar performance upgrades fpr the 4.0 that work well. A 4.7 stroker built the the limits of streetability can deliver 275 hp/ 300 ft lbs torque but are not cheep. Save your $ and do something that has a major impact.
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Old December 30th, 2012, 09:29 AM   #17
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Hard to beat a 8.8, same bolt pattern, discs, cheap, and strong IMHO. Not trying to beat you up, there's just ooooodles of threads on this discussion. It all comes down to ability and how deep the pockets are.
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Old December 30th, 2012, 09:34 AM   #18
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I've got a 98 TJ with the 4.0 & 5-speed and also run 33s.

4.56 is the right ratio for 33s - perfect, in my opinion. 4.10 isn't bad, and perhaps is a little better for a DD and highway MPGs but will not be good if you go over 33s.

My TJ came with 3.07s, and when I went from running 3.07s (where 5th gears was seldom usable) to 4.56s it felt (via the "butt dyno") like I added two more cylinders.

The 4.0 is already a pretty "hot" engine in stock form - there are few things (outside of a full stroker) you can do to it that'll get you a large gains for the cost involved.
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Old December 30th, 2012, 09:47 AM   #19
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I'm a cheap bastard and don't think I'll be investing in a stroker any time soon. I would like to run the axles I have for now with the advice of changing gears.
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Old December 30th, 2012, 09:53 AM   #20
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Good call. Maintains reliability as well.
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