2.5l XJ performance

[unclemonte]

Can anything be done to improve performance of the 2.5 ? This is a 96 XJ and its stock. Im brand new at this so pardon my ignorance. Can it be replaced with a 4.0 ?

 

[Beej]

Can anything be done to improve performance of the 2.5 ? This is a 96 XJ and its stock. Im brand new at this so pardon my ignorance. Can it be replaced with a 4.0 ?

Yes it can be replaced by a 4.0. Anything is possible given enough money and time D). I have also heard more than once though, that depending on availability of XJ's in your area, you might come out ahead to just sell the one you have and find one with the components and parts you want.
For performance mods to the 2.5 though, similar things that are done to the 4.0 are also done to the 2.5 with success:
Larger throttle body with spacer (4.0 TB swap is popular)
Better breathing cold air intake with high flow filter
Headers with a larger freer-flowing exhaust and cat
Upgraded ignition components (including 8mm or higher ignition wires & high-quality plugs)
Replacing the belt-driven fan with an electric will reduce some drag on the engine and apparently give higher horses at high rpm's
Advancing the timing slightly

More people will undoubtedly chime in here with more info, but this is what I have gathered over time. Its apparently good for about 25-30 more horses...

 

[j99xj]

I agree with Beej. The little 2.5 can perform better with bolt ons. However you're going to be wanting a 4.0 sooner or later, especially if you lift and install bigger tires.

I wouldn't bother with a 4.0 swap. Its much easier to just buy one that came with a 4.0 stock. They are very common and affordable in all parts of the country.

 

[Dr. Dyno]

I wouldn't bother with a 4.0 swap. Its much easier to just buy one that came with a 4.0 stock. They are very common and affordable in all parts of the country.

Agree. No matter what you do to the 2.5, it'll still be lacking in displacement and at best you might match the HP output of a stock 4.0 if you supercharge it. Better off to buy a 4.0 XJ in the first place and build that up instead. You could think about a tasty 4.6 stroker.

 

[old_man]

Speaking from experience, you can boost the 2.5L power to a point, but it will never be a hot rod. I took an 85 2.5l and converted it to tbi, bored it, ported it, added a cam and headers. It was significantly better and I never was at a loss for power wheeling, but it just wouldn't climb the mountain passes or hold 85 on the freeway fully loaded. I took my time and built a 4.7L stroker and swapped it along with the complete wiring harness and tranny. Boy what a difference.

I tend to like to do things the hard way, so I built it myself, but I would recommend selling your current rig and getting a 4.0L rig. It will actually be cheaper and a ton less work.

 

[CameronB]

Hey Old Man, I've got an 86 TBI XJ. Do you know if it's possible to use a larger TB? Did you use a stock-size TB? It seems pretty small to me, and I don't see how I can upgrade it at all.
I installed the air box/filter from my 95 4.0 and a cold air intake, but there's at least a .5" diff between the air box outlet and TB. Plus I've got a leak somewhere on my header. That may be why I'm not passing emissions. Which header did you use?

 

[unclemonte]

Thanks for the help

 

[Big Red]

I know 2.5L XJs are out there, but seriously how common are they? Do only the base models have them like in the SE, etc? Could a Laredo or Sport model have a 2.5L?

I've only seen a few XJs without a 4.0L emblem on them, unless 4 banger guys are being sneaky and putting on 4.0L emblems on their 2.5L XJs. :laugh3:

It is much easier to sell the XJ with the 2.5L and get a 4.0L like people have said here. A good selling point is you can say that the Jeep is good on gas and a XJ is a very practical vehicle. Show them the fold down seats and 4x4 for adverse driving conditions.
Jeeps just sell themselves. :laugh3:

Troy

 

[manuelxj]

i have a 2.5 in my 94 xj with, port and polised head, intake ,and exaust manifold. with 2.5"exaust pipeing out, 63 mm tb, tb spacer . soon to be adding a new block thats been bored .30 with all forged pistons, a mid-low range cam and a 75 shot of n20 ...lol yea i know im wasting my money but its fun and i like being the one thats diffrent..

 

[Big Red]

Seriously where are you guys finding these 2.5Ls? They are hard to find from what I gather unless you get the bone stock trim level and even then you can get a 4.0L. Stop wasting your $, sell that XJ and get a 4.0L, there is no way around the price in a conversion, it's just not worth it.

 

[old_man]

The early XJ's didn't even have a 4.0L option. As for bigger TB. If you don't go headers, and some head work along with a cam, it is doubtful the bigger TB will yield you much. For wheeling, adding a 9 pound flywheel weight made the biggest improvement.

I loved my 2.5L and its 25+mpg, but here in the mountains, it simply didn't have the lungs for the passes. I never was at a loss for power on the trails. I do know that when I went to the stroker, I sure started busting a lot more axles. I lost 2 within 10 minutes of eachother on simple obstacles.

 

[Big Red]

The early XJ's didn't even have a 4.0L option. As for bigger TB. If you don't go headers, and some head work along with a cam, it is doubtful the bigger TB will yield you much. For wheeling, adding a 9 pound flywheel weight made the biggest improvement.

I loved my 2.5L and its 25+mpg, but here in the mountains, it simply didn't have the lungs for the passes. I never was at a loss for power on the trails. I do know that when I went to the stroker, I sure started busting a lot more axles. I lost 2 within 10 minutes of eachother on simple obstacles.

Is the 9 lb fly wheel the same as the inertia ring that Tri-County Gear sells? I know they have some tricks up their sleeve with their 4 banger YJ with the Klune-V they were running in it. I think they have since retired this rig, but it can be seen on 24 hrs on the Hammers event a few years ago, it's the yellow and blue YJ.

Troy

 

[manuelxj]

as for where i am find them i have three motors in my yard right now lol my jeep that i drive a friend found in a used car lot picked it up for somthing like 1500 bucks ,one of the motors was in a 90 4 door xj that i got for a parts rig,the second spare motor was out of an 84 2 door xj that was hit in the rear ,and the last motor was given to me from some one that put a v8 in there yj...and right now there is 2 two door xjs for sale here in anchorage that have the 2.5 in them..i have had no problem finding them the 4.0 2 door xjs are rare up here for some reson ..im gona build the 4bannger up as far as i can then when i find a 4.0 2 door im gona up grade then lol not gona try to swap the motors just build another xj...

 

[MudDawg]

I have a well built 2.5 that works pretty good...gotta agree with Tom though, it ain't a rocketship on the road.but it does cruise good at 75 once it gets wound up...and there ain't any mountain passes in Florida. But put 'er in 4lo and lock 'er up, it'll go anywhere I have the stones to take it (within physical reality without tearing the body up). Other than the engine mods and 4.88 gears, the best mod for a 2.5 powered rig is to make it as light as possible...mine is completely stripped except for two seats, no massive rock bumpers or winch.....I know thats hard for you guys out west to understand, but all you need in Florida is a good snatch rope cause the only way you will get stuck is in the mud or sand.

I just bought another MJ...guess what engine?? A 2.5 of course:laugh3:

 

[85xjwoody]

I suppose I could chime in on this one. The 2.5 is a great motor. Can take a hell of a beating and still keep going. I don't use mine on the highway but when I do it does ok. On the trail in 4lo it works just fine. I broke three d35 axles before going with the 8.8 all with the 2.5 under the hood. I am not light on the gas either.
I got a 96 with the 4.0 a couple of about a month ago and I still prefer the 2.5. Yeah the 4.0 has more power but with the way I am with the skinny pedal I am already breaking shit. Much less room in the engine compartment with the 4.0.
All in all both engines are great and almost the same. In the end it is going to be how you wheel and what your preference is for what you need. Good luck with your choice on what to do.

Kim.

 

[61scout80]

i have found 2 of them, one is a 96 2wd 5 speed 4 door (bone stock) and the other a 94 4wd 5 speed 2 door (don't have it yet, but its stock w/ a long arm 6" lift, allied bead locks and a load of other goodies in the cargo area). the 4 door is going to become my commuter and the 2 door is going to be a trail rig. I have always wanted to learn about turbo systems, so i just might turbo the 4 door in due time, if i blow the thing to hell i'll only be out a few hundred bucks....