1998 Jeep TJ Engine Swap 2.5 to 4.0L - JeepForum.com
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post #1 of 6 Old 10-20-2014, 11:22 PM Thread Starter
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2012 JK Wrangler 
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1998 Jeep TJ Engine Swap 2.5 to 4.0L

Hi everyone, this is my first post on here, I currently drive a 2012 JK wrangler unlimited with some minor modifications, however things are becoming more and more expensive to fix after some serious trail running. I am picking up a 1998 TJ with a 2.5L engine and am looking into swapping to a 4.0, I have been doing some pretty extensive research but I would like some help, could anyone help me put together a list of things I need to change for this swap to work? Thanks a lot!

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post #2 of 6 Old 10-21-2014, 01:16 AM
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I bet it would be cheaper to just buy a 4.0 as most TJ's have that engine anyway. If you buy the 4 banger, just gear it low enough and leave the motor as is.
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post #3 of 6 Old 10-21-2014, 01:27 AM
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2000 XJ Cherokee 
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Swapping to a 4.0 will be just as hard as swapping in a 5.2L or 5.9L V8, everything has to change. The sweet spot for the 2.5L is 33s and 4.88 gears. In mine, I also plan to swap in a cast iron 4spd like a NP465 to get a granny low (advance adaptors makes an adaptor) and a gear driven case that I can run 4:1 gears in.

Great idea on getting an older jeep for the trail, why destroy a nice new one.
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post #4 of 6 Old 10-21-2014, 08:09 AM
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1998 TJ Wrangler 
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Posts: 26,297
Here is a thread you can check out:

2.5-4.0 swap is underway!!

I agree with the others, I'd either buy a 4.0 I6 or buy the 4 cyl and swap in a V8.
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post #5 of 6 Old 10-21-2014, 08:25 AM
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2006 TJ Wrangler 
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Buy the 2.5L (assuming it's the 5-speed) and keep it. I've put 230k on mine over the last 12 years and she's still going strong. She does everything I need her to do, (plow, tow, climb). She asks for more and never complains. This is from a guy who owns both the 2.5 and the 4.0.

Sorry, I know you want the 4.0 and probably for very good reasons, but I just love my little 2.5 so damn much.

I agree with others who have posted here; it will be much easier just to buy the 4.0 and probably no more expensive than buying the 2.5 and swapping to the 4.0. However, if you are interested in doing it for kicks and the learning process then all the power to ya. Many have done it and this is the right place to learn the ins and outs.

Good luck.

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post #6 of 6 Old 10-21-2014, 10:59 AM
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1998 TJ Wrangler 
Join Date: Nov 2008
Location: Longview, WA (one hour north of Portland, OR)
Posts: 3,616
x2 on 4.88 gears and 33" tires with the four cylinder/five speed. It is the sweet spot for these Jeeps. Unless you're doing crazy type four wheeling, this combo will do everything you want it to. Yeah; you might have to downshift on long uphill grades - it's not that big a deal. Off-road, engine size really makes no difference (again, unless you're doing crazy four wheeling stuff). The money you save not doing the engine swap can go to the gears and lockers (which you would probably be doing anyways even if you got a TJ with the six cylinder engine).

We took my four cylinder TJ (4.88 gears and 33" tires) up to Alaska and Canada for a few weeks towing a small trailer (and Jeep's rear seat removed for carrying luggage) with two large guys and had no issues. The 2.5 is a nice little engine.
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