To create the 6.1-liter version of the Chrysler Group’s HEMI, SRT powertrain engineers applied tried-and-true engine-building tricks honed by generations of American hot-rodders. They unleashed 85 more horsepower by adding more cubic inches, increasing the compression ratio, redesigning the cylinder head, intake and exhaust systems for increased flow, and increasing 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 exhaust headers with individual tubes encased in a stainless steel shell, all 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 3.5-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 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 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.