wow this thread went downhill fast.
personally, I liked the centri blower stuff I saw from RIPP. It looks like they complimented the 4.0L's already broad torque band pretty well. It doesn't have 300 ft-lbs off idle, but you wouldn't want that...especially in rock crawling & general trail riding. You'd be breaking stuff left and right, and you'd spin tires way to much. I'd much rather have 175-200+ ft-lbs at the wheels at 1000rpms, with a nice smooth increase to 300-320 ft-lbs plateau between 3200-3700rpm.
This is exactly my point, the Rubicon with the 4:10's and 31" tires isn't suffering down low, it is on the highway and acceleration that lack, this is where the centrifugal will shine in that truck.
the roots blowers make a lot of heat and need some way to cool the intake air, especially on a Jeep which already has high underhood temps. air-to-water intercooler, whatever, but I'd like to see under 120-140*F IAT in rock crawling and highway driving alike, regardless of ambient temps.
twin screws a pretty nice and offer slightly lower intake temps with increased efficiency over roots, but there aren't many kits that actually work for roots or twin screw on a 4.0L. Kenne Bell no longer sells their 4.0L kit, and Avenger does nothing for tuning, adding another $1000 to the cost for Unichip or FTC-1 with tune.
Twin screws actually generate more heat for IAT's especially since there mounted on the engine.
turbo's do pretty nice, and can be sized for a nice flat torque curve, but with the size turbo you use they end up choking around 4500-5200rpms (depending on altitude among other things) - see the "scrapinrocks" YJ turbo thread on here. his torque curve is very nice...but he's got distributor, OBDI with a FMU, which is easier to tune than a coilpack OBDII TJs.
and no matter which boosted way you go, you're still stuck with a weak cam. Now I suspect you could easily see 260 ft-lbs at the wheels with either boosted setup and a good cam from Comp Cams, Crane or Hesco. Still running 91/93 octane.