Engine

Powered by a 6.1-liter HEMI V-8 producing 420 horsepower (313 kW) and 420 lb.-ft. of torque (569 Nm), which adds 90 more horses and 25 percent more power than the 5.7-liter HEMI-equipped 2006 Jeep Grand Cherokee, the all-new 2006 Jeep Grand Cherokee SRT8’s performance numbers include 0-60 mph in less than 5 seconds, 0-100-0 mph in the low 19-second range, and 60-0 mph braking distance of less than 125 feet.

Powertrain

Providing horsepower and torque to the unique SRT four-wheel-drive system is a specially tuned version of the new 6.1-liter SRT HEMI engine. Inspired by the original family of HEMI engines, the SRT 6.1-liter HEMI employs the namesake hemispherical combustion chambers that provide power and efficiency, while retaining classic HEMI visual cues, including the orange-painted cylinder block and black valve covers.

SRT engineers who developed the Jeep Grand Cherokee SRT8’s engine achieved more horsepower by adding more cubic inches, increasing the compression ratio, and redesigning the cylinder head, intake and exhaust systems for better flow and increased engine speed.

For more displacement, SRT engineers bored out the diameter of the cylinders in the HEMI by 3.5 millimeters each in order to increase the total displacement to 6.1 liters from 5.7 liters.

Compression ratio was also increased to 10.3:1 from 9.6:1, increasing engine efficiency and power.

Engine breathing was increased with new higher-flow cylinder heads, a specially designed intake manifold and fresh air induction system, and exhaust headers with individual tubes encased in a stainless steel shell. All are unique to the 6.1-liter HEMI engine. Larger-diameter valves and reshaped ports in the heads allow for maximized air flow. The intake manifold was designed with larger-diameter and shorter runners for higher-speed tuning. Exhaust is routed through a large-diameter (2.75-inch vs. 2.5-inch) exhaust system with four-inch chrome tips.

To further increase horsepower, performance-oriented camshaft profiles were developed to allow more air in and out of the cylinders, as well as manage a higher engine speed. SRT engineers increased the HEMI’s peak power output engine speed nearly 20 percent to 6,000 revolutions per minute (rpm) from 5,000 rpm. Intake and exhaust valve stems are hollow, and the exhaust valve stems are filled with sodium to help dissipate heat more efficiently.

The high-performance SRT 6.1-liter HEMI is strengthened with redesigned components, including a reinforced engine block, forged steel crankshaft, high-strength powdered-metal connecting rods, floating-pin pistons (cooled by oil squirters), and an oil pan modified to manage oil return to the pan sump at high engine speeds.

Power from the SRT 6.1-liter HEMI is sent through a special torque converter to an SRT-upgraded five-speed automatic transmission. Torque is then sent to front and rear differentials through a specially designed transfer case.