Page: [1] [2] [3] [4] [5] [6] [Exterior] [Interior] [Engineering]

Renewed HEMI V8

Dodge has updated the Ram’s popular 5.7-liter HEMI V8.

Scott Kunselman, Chrysler’s vice president of body-on-frame products, says, “We renewed the HEMI powertrain. The basic architecture is the same but we’ve improved the HEMI’s power, torque, and refinement.”

On paper, the power output of the HEMI has risen from 345-horsepower and 375 pound-feet of torque to 380-hp and 404 lb-ft. Several key technologies have been added.

Officially, the revised HEMI adds Variable Valve Timing (it actually uses a specific version of VVT, called Variable Camshaft Timing) that’s typically used in dual overhead cam (DOHC) engines and only recently in overhead valve (OHV) pushrod engines, like the HEMI. VVT phases the camshaft to control intake and exhaust valve timing, for better engine performance at all RPMs and improved emissions.

A new active intake system controls the lengths of the intake manifold’s channels, shortening the intakes at lower RPMs for more torque and lengthening the intakes at higher RPMs for more power.

The HEMI’s Multiple Displacement System (MDS), which shuts off half the engine’s cylinders to save fuel during steady state driving conditions, has been improved to work across a wider engine load. At highway speeds it now works over 70 miles-per-hour. MDS in the 2008 model only worked up to 65-mph. The new MDS gives the Ram a 4% bump in fuel economy and extra torque when the engine is in 4-cylinder mode.

“We’ve spent a lot of time finding the correct balance between fuel economy and engine performance. We looked at the cam timing, active intake, operating ranges, power needs, and noise, vibration, harshness challenges and tried to balance it all for the customer,” says Mr. Kunselman.

There are also some key differences in engine cooling for the new HEMI. The 2008 Ram placed the condensers side by side but the new truck uses older fore-aft stacking. And the inlet in the grille has been optimized for both better cooling and aerodynamics.

Other Powertrain Changes

The 2009 Ram shares its flex fuel Magnum 4.7-liter V8 with the midsize Dodge Dakota. The 4.7-liter V8 was recently updated to a HEMI-like setup of two spark plugs per cylinder and has improved airflow through the cylinder heads. It’s rated at 310 horsepower and 330 lb-ft of torque. Unlike the HEMI, the Magnum V8 does not have MDS for improved fuel economy.

Both V8 engines use the Ram’s carryover 545RFE 5-speed automatic transmission. Dodge has added Electronic Range Select (ERS) to the transmission, which enables the driver to manually limit the highest available transmission gear, allowing manual upshifts and downshifts based on road speed and engine speed.

The base engine is a 3.7-liter V6 rated at 215-hp and 235 lb-ft of torque. It comes with a standard 6-speed manual transmission or 4-speed automatic. The 4-speed automatic also gets ERS like the V8 engines and, interestingly, tow/haul mode.

Page: [1] [2] [3] [4] [5] [6] [Exterior] [Interior] [Engineering]