Mainstream Grand Cherokee models equipped with the optional 5.7-liter Hemi V8 combine satisfying acceleration and handling on the pavement with the kind of serious off-road prowess that has become a Jeep trademark. In fact, our review last year declared that the changes to this third-generation model have made it “nothing less than the best Grand Cherokee ever.”

Now, of course, we get to eat those words thanks to the engineers of parent company Chrysler’s Street & Racing Technology (SRT) division. The SRT folks have thoroughly transformed the Grand Cherokee, giving it everything from a larger Hemi engine with nearly 100 more horsepower to a handsomely restyled interior to twin four-inch center-mounted exhaust tips that look like they could spit flame every bit as well as Batman’s original set of wheels. While the 2006 Jeep Grand Cherokee SRT-8’s more muscular styling may be the first thing that catches your eye, it’s the mechanical modifications that leave the most lasting impression.

At the top of that list is the 6.1-liter Hemi V8 engine that puts out 420 horsepower and 420 lb.-ft. of torque. To create it, engineers started by giving the familiar 5.7-liter Hemi a 3.5mm larger cylinder bore and bumping the compression ratio up from 9.6-to-1 to 10.3-to-1. Redesigned camshafts and cylinder heads plus larger diameter intake and exhaust plumbing further open up the big motor’s breathing. A reinforced cast-iron block and stronger internals help the engine stand up to the abuse that’s bound to come with increasing the engine’s redline from 5,000 to 6,000 rpm.

Power is sent to all four wheels via a five-speed automatic transmission with a manual-shift feature and a unique transfer case that combines components from two different units for lighter weight and better power-handling capability. This system – the first four-wheel-drive set-up ever used in an SRT vehicle – sends 95 percent of available torque to the rear wheels under normal driving conditions and can transfer as much as 100 percent up front when those back tires lose their grip. A heavy-duty driveshaft and beefed-up Dana 44 rear differential round out the powertrain upgrades.

Additionally, specially-tuned shocks, springs, and larger sway bars noticeably improve the Grand Cherokee’s already respectable handling. The modifications also lower the vehicle by an inch all around for a lower center of gravity, reduced aerodynamic drag, and a more aggressive stance.

The steering gear and brakes have been similarly tweaked. The power rack-and-pinion steering has been given a slightly faster ratio, while front and rear disc brakes are both more than an inch larger and use four-piston Brembo brake calipers and pads. For a finishing touch, standard 20-inch aluminum wheels are fitted with fat Goodyear Eagle all-season run-flat rubber. Those tires – 255/45 up front and 285/40 in the rear – also carry a W-rating, which means they’re good up to 168 mph.