Doug Henry Tarboro, Rocky Mount

GM has just unveiled its newest motor that will be placed in the Chevrolet Silverado's and GMC Sierra's heavy duty truck lines. Why the need for a new round of updates to the Duramax just three years after the current engines arrived? Come Jan. 1, 2010, all new diesel-powered vehicles will have to meet tougher federal diesel emission standards that will reduce allowable nitrogen oxide levels by 90 percent from today, 96 percent from 1994 levels. Nitrogen Oxide is a major air pollutant that contributes to smog, asthma, and respiratory and heart diseases. It's a byproduct of diesel's high combustion temperatures. The new Duramax diesel engines are built to meet new clean-air regulations, plus they feature other key improvements in technology and capability. Like today's Duramax, the Isuzu-GM joint venture engine will continue to be available in two versions. "The new Duramax diesels are based on the same engines that have been around since 2001," said Gary Arvan, a GM diesel powertrain engineering chief. "The 2500 and 3500 Chevrolet Silverado and GMC Sierra HD pickups receive the high-power LML motor [replacing the 2007-10 LMM], while the 2500 and 3500 heavy-duty vans receive the lower-rated LGH engine [also replacing the LMM]. Both have iron blocks, aluminum cylinder heads, and their [6.6-liter] bore and stroke are unchanged." The LML will be paired with an Allison six-speed transmission while the LGH will be mated to GM's in-house 6L90 six-speed gearbox, which is also matched with the 6.0-liter V-8 gas engine. The two biggest technical changes Arvan shared details about are the Duramax's all-new selective catalytic reduction and its enhanced exhaust gas recirculation systems -- which are needed to scrub Nitrogen Oxide down to no more than .2 grams per horsepower/hour -- as well as its approved use of B20 biodiesel. That's 80 percent ultra-low-sulfur diesel and 20 percent biodiesl.

NOx selective catalytic reduction uses diesel exhaust fluid. The urea-based solution (32.5 percent industrial urea and 67.5 percent deionized water) is held in a 5.5-gallon storage tank and injected as a fine mist into the Duramax's hot exhaust gases. The heat turns the urea into ammonia that -- when combined with a special catalytic converter -- breaks the NOx down into harmless nitrogen gas and water vapor. NOx selective catalytic reduction uses diesel exhaust fluid. The urea-based solution (32.5 percent industrial urea and 67.5 percent deionized water) is held in a 5.5-gallon storage tank and injected as a fine mist into the Duramax's hot exhaust gases. The heat turns the urea into ammonia that -- when combined with a special catalytic converter -- breaks the NOx down into harmless nitrogen gas and water vapor. Arvan says diesel exhaust fluid refill intervals will vary depending on duty cycle. Some customers will only have to refill during routing maintenance, such as when the oil is changed, while others will have to top off the tank sooner. To ensure that the exhaust fluid tank is refilled, Duramax-equipped trucks will warn the driver when the fluid is down to a 1,000-mile range. A series of start-up warnings -- including lights, chimes and messages -- will become more frequent until the tank is empty. If the driver continues to operate the truck with a dry tank, after a final warning and restart the truck will only operate in a "limp-home" mode that limits speed to just 5 mph until the tank is refilled. The LML and LGH also make greater use of exhaust gas recirculation across the Duramax's power band than did the LMM Duramax. The system recirculates a portion of the engine's exhaust back into the engine at a lower temperature. The cooled gases have a higher heat capacity and contain less oxygen than air, lowering combustion temperatures and reducing the formation of NOx. Exhuast gas recirculation is prevalent in today's clean-diesel engines to reduce NOx, but it's not efficient enough in its current form to meet 2010 emissions levels in GM's trucks, hence the use of selective catalytic reduction also. "We've improved the performance of the Duramax in the van to 250 horsepower and 500 pounds-feet of torque from today's 250 hp and 460 pounds feet," Arvan said. "We aren't prepared to talk about the new power figures for the heavy-duty trucks yet, but we won't let the new emissions regulations bring us down [in power]. We'll produce at least the 360 hp and 660 pounds-feet of torque [with the LML] that we make with today's engine."

The LGH Duramax has a smaller exhaust gas recirculation cooler than the LML motor because of its lower power ratings. It also has a smaller radiator and cooling system.Efficiency improvements to the recirculation system include new separate cold and hot circuits that allow exhaust gas to recirculate immediately after engine startup, when engine temperatures are still relatively cool and when the engine is idling.In addition to burning cleaner, the LML/LGH Duramax can also burn greener. It's certified to burn B20 biodiesel, up from the LMM's B5 rating. "We made a lot of enhancements to make sure the new Duramax is robust with biodiesel," Arvan said. "The engine uses our latest-generation fuel filter that includes a coalescing filter to trap any water that could be present in the fuel. The downstream injector [behind the exhaust] for diesel particulate filter regeneration means we also won't have a worry of oil dilution with B20 fuel from in-engine post injection [like is used on the LMM diesel]. There's also additional heating to the fuel circuit so the filter won't get plugged from old [B20] fuel gelling or waxing." Another big change to the Duramax's fuel system is the first-time use in the Duramax of piezo electric injectors, which can react faster to fuel demands than the old solenoid injectors could. Fuel pressures are up from 1,800 bar (26,000 psi) to 2,000 bar (29,000 psi) for improved fuel atomization and combustion control. The Duramax also continues to use a conventional gray iron engine block, but it's been structurally enhanced around the lower skirt to help reduce noise, vibration and harshness. Combined with a new pre-combustion fuel-injection scheme that injects two pilot injections into the cylinder before the main injection, noise levels have been reduced up to 50 percent in the 1,500-1,600 rpm peak torque operating range. Another change is reduced engine-idle speed. Arvan says it's been reduced from 720 rpm to 640 rpm in the pickups. The van is able to idle at only 600 rpm. Arvan also says fuel economy will remain the same -- a key concern of any new diesel owner given the emphasis on clean emissions over operating efficiency. A key concern to many owners may be whether or not the new engines will be the same on gas mileage and the word on the street right now is that it will be the same if not better.

We here at Doug Henry Chevrolet of Tarboro are a short trip from anywhere in Eastern North Carolina located right off HWY 64 in Tarboro, NC. We're the North Carolina Silverado Dealer Located in Tarboro.  We have the largest variety of in-stock silverado's and also have a huge selection of pre-owned inventory, that will surely meet your needs for any vehicle. In addition with our acquisition of Team Ford Sales in Tarboro, we are pretty confident we can get you in the ride you want at the right price. So when those big town dealers don't treat you right come on down to Doug Henry Chevrolet of Tarboro.