Big bore HEMI 6.1L on Run Flats
This vehicle is alarmingly quiet at idle, then ramps up to any level of banshee scream you can imagine from the big brother to the 5.7-liter Hemi. Goodyear Eagle 255/45ZR20 high-speed run flat Tires are sucked onto 20-inch tall aluminum Wheels ten inches wide for needed traction. When you drive this rocket, you’ll immediately appreciate how well this suspension is thought out and Tuned with regards to keeping the vehicle planted on the asphalt.
Bilstein mono-tube shocks and suspension tuning from Mercedes Benz German engineers work with Quadra-Trac Active On-Demand 4WD system. Brembo big-rotor disc brakes with enormous calipers and Anti-lock technology are definitely items you don’t have to upgrade. A Dana 44 rear differential with beefed up ring and pinion gears and a new axle housing are sufficient for a starting point. But the actual baseline horsepower and torque available with this particular HEMI can put some strain on any Dana 44. If a Dana 60 were shoehorned under that rear Grand Cherokee deck, it would make more sense. A bomb-proof Ford 9-inch would work, but that would be bloody treason. 
Front end components and tuning are similar to the rear with the exception of 20x9-inch big spoke aluminum Wheels and 255/45R20 run flat Goodyear Eagles. Brembo brakes manage the big five-spoke Wheels up front as well. It’s easy to dismiss the body cladding and ground effects, but there again, you’ll value it when you drive it.
Bucket seats are necessary to hold you into the potential cornering ability and flat line trajectory this hot rod is capable of. In fact, one of the clearest accolades we can bestow upon this turn-key muscle puppy is how diligently, and with the greatest degree of safety possible, the Jeep SRT-8 product development team, Dodge performance, and the boys of Benz packaged this hot rod.
Rated at 415 to 420 horsepower and similar torque figures, this engine runs 10.3:1 compression on super unleaded pump gas. The 5.7-liter platform was bored 3.5mm at each cylinder; the Cylinder Heads were smoothed, polished and warmed up to increase flow. Traditional tube Headers are Tuned just for this engine and housed behind an aluminum shield. Intake manifold runners are larger in diameter with shorter runner to allow the engine to reach and run at higher speeds. And reach it does.
The engine block is painted orange and the valve cover are black just like the early Hemi mountain motors that intimidated the quarter mile drag strips at places like Lions, Irwindale, and Pomona. Altogether, the 6.1L turns in about 85 more horsepower than the 5.7L. We hear those Cylinder Heads are not, indeed, true hemispherical chambers like the Hemi heads of yore. If that’s the case, this is a performance engine with too much potential not to appreciate it as different animal on its own merits.
Our seat-of-the-pants impression is a well earned thumbs up! Steering is precise, but a little twitchy until you get accustomed to the tuning of the steering, fat tires, and firm suspension. One really needs to get accustomed to this vehicle as a false sense of security would be unfortunate with this kind of performance capability. Anyway, that twitchiness is experienced under full throttle with enough room to let the HEMI scream. The tach will wind up most ricky tick backed by equivalent forward motion and a zero to 60 MPH said to be around five seconds. That’s cool, we didn’t put a stop watch to it, just watched that speedo flush past 90 before easin’ ‘er down for the left hand sweeper and preservation of a clean driving record. 
No doubt, this power package is a formidable performance engine bolted to an equally well matched five speed automatic transmission with a manual shift option. With the manual shift option, you must remember that when you come to a stop sign the transmission automatically shifts back to first gear. You need to be aware of this little bit of information because the mind instantly forgets you were just in selective manual mode, then gets ready to plant and launch for another quick pass through the gears in automatic and…oops, you just hit the rev limiter in first gear. Embarrassing once, stupid twice, and if you can’t get it straight after that, just leave it in auto. 
Acceleration from a stop is hard, and you feel the lateral pull of torque under any launch scenario. At freeway speeds, acceleration is also very strong and responsive to throttle input. But that’s about what you’ll get with the 2006 Jeep Grand Cherokee, a 400 plus horsepower store bought vehicle wearing sheep’s clothing.
Fuel economy was not the point of driving this SRT-8. We didn’t expect great miles per gallon, and we didn’t get it. A tank of high test gave us a little more than a 250 mile range. It was simply too much fun driving this vehicle to settle down on the throttle with only a week to live with it. No, we didn’t play rough or reckless; we just experienced a new level on the JEEP brand fun factor dial. This vehicle is a true performance capable SUV with four seats and some room in the back for golf clubs and some luggage. That’s it. Use this one for road trips, ski trips, fishing trips, or the daily commute. If you can afford super unleaded fill-ups more often than not, consider this one. More so, if you seek the human need for speed and a smile every time you scan the horizon before a smash and dash, check out this 2006 Jeep Grand Cherokee SRT-8.
Our test machine listed for around $45.5K but they start at $39K. Compare that to the other higher performing options out there, then ask your self: ‘what other vehicle can run this hard, yet allow me to drive through a snow storm?’ That should narrow down the field.
And, it’s only fair to point out; four hundred-plus horsepower in a production vehicle is not extraordinary. However, short of a supercharger – imagine that on this engine __ it has not been a common option for a factory V8 in more than 25 years. This motor and drivetrain performance is sheer hardware, engineering, and packaging that uniquely identifies this vehicle as the most powerful Jeep ever offered to the public. A new day has dawned for muscle performance of all kinds, so we thought we’d share a few photos at sunrise.
 |  |  Jeweled (automatic on/off) headlamps work with the scalloped body lines to give an aesthetically cool look to proven function. |
 Power adjustable pedals are performance piece you might not care to upgrade. |  From the rear, the wise must be wary. Big 2.75-inch dual exhaust pipe meets in the center where the spare tire would normally go. |  Here you can see the lateral support wings of the 8-way power adjustable front seats. Up front, we had plenty of leg room and road trip comfort. |
 |  |  Dual exhaust is strictly functionality that just happens to look great. The Dana 44 does run a shored-up ring and pinion gear set, but more “live-ability” is suggested here. |
 |  Seven gill grille identifies this rig as a 2006 Jeep Grand Cherokee. Ground effects, fog lights, and jeweled headlights don’t tell the average motorist how potent this vehicle is. | |
