Sooner or
later your Fortwo driving friend is going to find themselves in the
desperate position of asking a pickup truck owner to help them to either:
a) move houses, or b) pick up a pizza in any position other than vertical.
Who’s
going to look Smarter then? Better
hope you’re friend has a Dodge Ram 2500 for the really big stuff.
The
2007 Dodge Ram Heavy Duty we drove is a marvel of engineering and load-carrying
capability. As Ford and General Motors powertrain
engineers breathe a temporary sigh of relief after having met this year’s
strictest diesel emission rules ever, with their new 8-cylinder Powerstroke
and Duramax diesel engines, the Chrysler Group is bragging loudly that
its new I6 Cummins-sourced diesel meets even tighter 2010 limits today.
It’s
also the Chrysler Group’s first BLUETEC-badged vehicle. BLUETEC
is DaimlerChrysler’s brand name for a suite of post-combustion
treatments in diesels, ranging from selective catalytic reduction (SCR)
to urea injection to soot traps to clean the particulate and nitrogen
oxide (NOX) emissions produced by lean burning compression ignition engines.
In
meeting the 50-state compliant ‘Tier 2 Bin 5’ exhaust
requirements, Dodge and Cummins reduced soot and NOX emissions by more
than 90% over 2006 levels - to .01-g/mile and .05-g/mile respectively.
For our EU readers keeping score, these numbers beat the less stringent
Euro 6 diesel emission limits that don’t go into effect until 2014.
There are no current plans to bring the Fortwo CDI to the U.S. because
the Euro and Canadian version aren’t designed for Tier 2 Bin 5.
To
clean the Ram’s breath, a diesel particulate filter (DPF) is
used to trap and incinerate soot like a self-cleaning oven. Small,
metered amounts of fuel are injected into the exhaust stream to raise
temperatures to the point where the particulates trapped in the DPF burn
up in a process called regeneration. This approach is pretty straightforward
and also shared with the GM and Ford oil burners.
NOX is reduced
using several complementary methods. Lower combustion
temperatures means less NOX, so a larger exhaust gas recirculation (EGR)
system and specially designed piston champers are used to keep cylinder
heat down. An electronically controlled variable geometry turbo (VGT)
provides near lag-free turbo response with sixteen fixed vanes, a sliding
yoke, and electric valve. A compressor wheel moves along the turbo
shaft to make the compression housing smaller, which makes it spin faster
at slow engine speeds for better performance. But it’s the
use of Cummins’s newly developed ‘Adsorber’ catalyst
to soak up remaining stray NOX molecules that enables the Dodge’s
emissions to beat Ford’s and GM’s tailpipe exhaust figures
and also comply with full 2010 Tier 2 Bin 5 standards.
Finally,
the 6.7-liter engine’s increased displacement makes up
for any power lost to the extra emissions equipment and lower combustion
temps. Towing capacity is actually boosted by 500 lbs over the
outgoing 5.9-liter Cummins I6 motor.
Both the
Ram 2500 and Smart Fortwo use a Bosch-sourced high pressure common
rail injection system to deliver measured squirts of diesel into the
cylinders so that noise is minimized and power maximized on a variable
basis. Not that size matters in all cases but Smart drivers might feel
a little shy in the locker room knowing that their common rail is about
one quarter the size of Dodge owners.
The 2007
Dodge Ram shifts gears with a new 6-speed automatic transmission
that can finally handle the full power output from the Cummins. Earlier ‘High
Output’ versions of the Cummins diesel were only available on trucks
with six-speed manual gearboxes. The 68RFE auto selector also
provides the Ram with a tow/haul mode for descent control on steep grades.
The Cummins
certainly sounds different from previous Ram heavy duty pickups when
you start it up. It’s substantially quieter
than the old 5.9-liter but clatter is still a few decibels higher than
the Duramax, our current benchmark for three-quarter and one-ton diesel
noise volumes. The lower noise levels are achieved through new
engine mounts, an engine block shield, and crankshaft counterweights
to reduce the diesel’s din during acceleration.
