you'll need a different tranny and transfer too.. they are different on the 4.0's.
dont forget that you'll also need new computers, sensors, fan shroud, drill new holes for the tranny mount, motor mounts and a starter.
in other words....either live with the 4 banger or swap in a v-8 for the same amount of work...or sell it and get a tj with a 4.0
I've always wondered why they went to the expense of building a different drivetrain to put behind the 2.5. It's got to have cost more than just configuring the bolt pattern to match the 4.0. Go figure.
You can tweek more out of the 2.5 and still be emissions legal. It will cost much less then other swaps. Now it will never give you the torque of the 4.0 or other swaps (as you will hear on this board "There's no replacement for displacement"[img]images/icons/smile.gif[/img] and short of a supercharger ..it's true)...but it can be made to get the job done.
Still the best thing that you can do is put in gears. 4.88s are available for the D35 and D30 and unless you are going bigger then 33" tires AND you aren't intending to be "hard core" and try and leap tall boulders in a single bound ..you'll do fine. 4.88s with 33" tires is almost exactly what a SE is set up stock with an automatic (3.73 gears are in the auto SE not 4.10s like your manual) and 205/t7r15 tires. You'll turn the same 3000 rpm @70+/- mph. This can run you easily $200-$250 per axle in labor ...but compared to an air tube and an expensive Borla exhaust (power chip/throttle body/ignition upgrade, etc.) ..you will see much more out of the 2.5. In fact dyno tests articles in JP mag showed that virtually every bolt on mod -especially the exhaust - cost torque in the 2.5. After over $1000 in bolt on mods they yielded something lke 3 hp and lost torque at some stratospheric rpm (like over 4000+). You can get a larger throttle body ..and you will perceive more power with less foot ..but will realize no REAL gains in power in daily driving unless you are fond of the upper rpm ranges at WOT. The power chips are also an option but I think that the best thing that they do is make some vendor's wallet very fat and your's much thinner. Some of these mods make sense on otherwise stock late model street racers. They may actually hit the speeds that these things allow more power to be developed at.
You're mainly looking for "drivability" for street/daily driving use. Except for the more advanced challenges, your low range should give you enough torque to conquer most things that you encounter. Unless your doing H8 olympic class activities you will do fine[img]images/icons/smile.gif[/img].