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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.

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