In 2011, the Ford Super Duty pickup will have a new diesel engine. It doesn’t have overhead cams actuating the valves, it has pushrods. It doesn’t have two separate turbochargers, it has one…sort of. The exhaust manifold isn’t on the side of the engine block, it’s in the valley where most engines have their intake manifold. Have Ford engineers gone mad?
Not really. The 6.7-liter Power Stroke diesel (codename: Scorpion) is lighter, stronger, has more torque and horsepower, better fuel economy, easily meets the extremely stringent 2010 emission standards for diesel, and it’s quieter—much quieter—than the engine that preceded it. All it took to do this was some good old-fashioned engineering.
The Highlights
- Compacted Graphite Iron (CGI), a material that is two times stronger than the gray cast iron previously used, allowed engineers to make the walls of the engine block thinner without sacrificing strength.
- Like a high-performance engine, the Power Stroke’s block uses a deep skirt design and cross-bolted main bearing caps for durability and reduced noise, vibration and harshness levels, and the oil pan is a structural member to keep lower block flexing to a minimum.
- The aluminum four-valve cylinder heads use six head bolts instead of four and have a higher clamping load, but also utilize a dual (upper and lower) water jacket to keep the valves cool and homogenize temperatures to eliminate hot spots that could lead to pre-ignition of the fuel.
- Actuating the valves with pushrods instead of overhead cams cuts cost without sacrificing performance. Since this engine turns at lower rpm than a passenger car motor, the high-rev capability of an overhead cam system is redundant. Better to move the V8’s 32 valves with a robust pushrod system.
- Swapping the position of the intake and exhaust valves made it possible to greatly reduce the length and volume of the exhaust system. This cuts down pumping losses, reduces the time it takes exhaust flow to reach the center-mounted turbocharger, and makes it easy to push the compressed intake charge through the air-to-water intercooler and into intake manifolds mounted on the side of the engine. (BMW uses a similar system on its twin-turbo gasoline V8.)
- The Honeywell sequential turbocharger houses a double-sided variable-vane compressor wheel mounted on a single shaft. Each side has a different profile, and is fed by a bifurcated duct. The first compressor scroll spools up boost more quickly while the second provides boost from the mid-range to redline. Variable-vane technology alters the angle of the compressor vanes to make the best use of the incoming air, and smoothly transition from one side of the turbo to the other. As a result, the unit acts like separate sequential turbos, packages in a smaller space, and uses fewer parts.
- Third-generation Bosch piezo-electric fuel injectors give greater control over the injection of diesel into each cylinder. By using two short high-pressure “pilot” injections and one main injection, engineers were able to greatly decrease the “death rattle” sound large diesel engines make by spreading out the ignition process. Interestingly, the Power Stroke’s combustion process is so complete there is no need for diesel to be injected after the main squirt (known as post-injection) in order to reduce soot emissions. This makes the Power Stroke’s combustion process cleaner than some passenger car diesels.
- A two-step exhaust-gas recirculation system lowers exhaust gas temperatures so a higher percentage can be added to the intake charge. In addition, the lower temps also reduce nitrous oxide (NOx) emissions.
- Emissions are treated in a three-step process that includes a diesel oxidation catalyst, selective catalyst reduction (injecting a spray of 67.5% water and 32.5% pure urea that vaporizes into ammonia and carbon dioxide into a catalyst where it is converted into nitrogen and water), and a diesel particulate filter to trap any remaining soot. Mercedes drivers will recognize this emissions systems as Bluetech, though Ford would not say if it also uses Bosch as a supplier.
The 2011 Super Duty engine is 160 lbs lighter than the engine it replaces, and will be built at Ford’s Chihuahua, Mexico engine plant. Though the engineers say the new Power Stroke has survived 250,000 miles of durability lab testing, 30 days at maximum speed and boost, 2,600 below-zero starts, thermal shocks from alternating hot and cold fluids in a running engine, and a 10-year arctic-use simulation, they also are proud of the fact that they have reduced the time necessary to service items like the turbocharger, exhaust gas recirculation cooler and high-pressure fuel pump by an average of five hours. That will make it much easier on the fleets that typically buy turbo-diesel heavy-duty pickups. However, we’d sure like to take lead engineer Adam Gryglak up on his claim that all of these technologies could be applied to a more compact diesel that could be used in light-duty pickups and large passenger cars.
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