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]
|
