What about the pentastar tells you it's good to 400hp? Anyone tear one down yet?
It'll be harder than you think-1, there isn't a large aftermarket crowd to make it worth while and 2-the exhaust manis are cast into the lower block. Thatll make for some fun piping.....
Rear undermount turbo comes to mind. In a JK, it wouldn't be too easy to fit a turbo under the hood. You can probably get it under the motor, but that may kill some valuable ground clearance. I haven't spent too much time underneath the truck yet (too damn cold) but I will in the spring. A nice small turbo will allow the motor to gain an easy 100hp, 100tq, and another 10mpg without breaking a sweat. Gas mileage is dependent on one thing, and one thing only, the TPS. The throttle position sensor dictates to your injectors how much fuel to dump. Since the JK isn't "that powerful" you need to bury your foot deeper into the carpet to get the car up to speed, moving, maintaining speed, etc. With a turbo, there is far more power everywhere, thus requiring LESS gas to keep the momentum going. On my s2000, after I went with a turbo setup, I instantly gained 10mpg, can easily pass in 6th, and doubled the wheel horsepower. I went from 183whp to 400whp. Not bad, while getting 35mpg. The car OEM is rated at 24.
As for aftermarket demand, luckily for us, Chrysler stuck this motor damn near into every production car they make. There is a market there, trust me. Someone will jump on it.