The JK is associated with a lot of words, but powerful isn't one of them. Especially when you put 42" tires, and weigh it down with steel bumpers, bigger axles, etc. The 3.8 and 3.6 simply don't have what it takes to effectively move that much steel and rubber down the road. Sure you could throw on forced induction like a supercharger, but for the expense you might as well swap in a bigger motor.
Why not go diesel?
Of course you see cummins swaps in JK's, but rarely do you see a Duramax swap. The Duramax is a great choice. Its a extremely reliable, powerful, fuel efficient, and a common engine to source. These reasons alone gives it great appeal. But paired with the Allison transmission is really what sets it apart from other Diesel Engines.
A group of engineers that i'm associated with has successfully swapped in a Duramax Turbo Diesel, with accompanying Allison Transmission in to a JK Wrangler.
*The Engine, Allison Transmission, Tcase, and rear axle are out of a 2004 Chevy Silverado. The engine is stock with the exception of a Airdog lift pump, 4" down pipe, and a 5 stage tune controller.
*The front axle is a Dana 60 with upgraded shafts.
*ARB lockers front and rear
*Custom long arm suspension that stretched the wheel base about 6". Rear is a 4 link. Front is a 3 link + Panhead bar.
*Hydraulic assist steering, with 2 speed anti-sway bar on front.
*42" tires
*Poison spider armor and fenders.
42” tires is the “why” behind putting a Duramax in a JK. 42” make it easy to roll up big rocks, yet on the street it is unbelievably peppy. It is surprisingly good on the trail and the street. When they were building it I thought it would be a nice circus freak for SEMA, but after driving and taking it offroad, I couldn’t believe how well-mannered it is on street and how capable off road it was. You don't notice the extra weight of the engine. It performs absolutely flawlessly, and puts a grin on your face every time you get behind the wheel. The power is refined, yet it doesn't ever seem to run out of it.
Because of how great this swap ended up, my engineering associates are considering developing a Duramax swap kit. They are just trying to gauge what kind of interest there would be.
So, what are your thoughts?