Where we spent most of our time was trying out the new diesel. The previous Power Strokes had been built by Navistar International for Ford, but after several disputes and lawsuits, that relationship soured. The diesel in the 2011 Super Duty represents years of work in-house, using some technology from Ford Europe but designed with heavy-duty work in mind. The new diesel offers 390 horsepower and 735 pound-feet of torque -- both best in class-improvements of 40 horsepower and 85 pound-feet. Ford also reduced engine weight with the use of a compact graphite iron block, but made the block stronger in the process: CGI is said to have twice the strength of gray iron, which is typically used in iron blocks. The engine also uses aluminum heads.
Power Stroke's engineers designed the layout to make it easier to manage noise and vibration, and the end result of their work is a modern diesel you can't hear from a distance and that doesn't fill the cabin with noise. Yet it's also much more powerful than before -- pulling away from traffic lights almost like a heavy-duty hot rod. And the new, B20 biodiesel compatible engine comes with an exhaust brake.
Federal regulations for 2010 create a new, significantly stricter requirement for diesel emissions, so it's no coincidence that the new 6.7-liter Power Stroke is dramatically cleaner -- producing less NOx-than before. This engine uses multiple technologies to reduce emissions, starting with exhaust gas recirculation. Some of the exhaust gases are cooled by engine water at about 90 degrees Celsius, and then routed into a low-temperature loop, a second cooling system in the engine that operates at about 50 degrees C (and also serves as added transmission cooling). The cooler inert gases displace oxygen and lower combustion temperatures, which together reduces the amount of NOx that's produced in the cylinder. This EGR system uses a hot-side valve, before the cooler, to reduce the amount of deposits that can get into poppets and seals, improving durability and reducing possible warranty issues.
The rest of the emissions work takes place after the fact, in the exhaust system. At the diesel oxidation catalyst, hydrocarbons are heated and converted into water and CO2. The heat created helps make the rest of the system's emissions reduction process more efficient. In the next phase, selective catalytic reduction, diesel exhaust fluid, a mix of urea and water, becomes CO2 and ammonia when heated. When the ammonia mixes with the exhaust gases and is exposed to the catalyst in the SCR system, what NOx was produced during combustion is converted into nitrogen and water. The diesel particulate filter traps any soot that was produced, and burns it away (called regeneration), when the soot trap is full.