ALL you guys that are looking for more performance from a 4.0. tear down the engine and blue print it. You might gain a little from that. Polish your intake runners, port the heads and intake , exhaust. You might gain a few extra ponies from that, change injectors, Clean up what the factory did not do to make the engine to it's max power. Then when you get all said and done you have spent better than 2 grand on the motor or more. You still have a 4.0 that might run a little smoother have just a touch more power and a little better torque curve.
A 89 yj with a 4.0 aw4 sye out of an 92xj. Now the hard part is done time to get it up in the air just a bit. Working on 8.8 with 3.73 and lsd for the rear. and new D30 hp with 3.73 .
For those who have not figured this out I'm old school but can handle the new too.
im just cheap, and cheap makes you creative.