Manufacturers say EPA-driven changes yield better fuel economy and other benefits.

The 2010 drop in NOx to 0.2 grams has been accomplished by most truck makers with selective catalytic reduction. Even with SCR’s requirement for adding diesel exhaust fluid, SCR has brought basic improvements.

Steve Duley of Schneider reports only one incident of DEF going into the diesel tank, and the problem was fixed with minimal downtime. It happened because the restrictor in the filler neck had fallen out.

That’s because letting SCR handle much of the NOx means less exhaust gas recirculation. Reducing EGR means the cylinders will need to contain less pressure, inviting modest performance and fuel economy improvements.

Torque curves are improved, too. Schneider National Vice President of Purchasing Steve Duley notes that “the engine manufacturers have taken advantage of having injection pressure available at any time during or after the compression stroke. Drivers report better acceleration and quieter running engines… Drivers like the power and overall performance.”

In Cummins’ case, the reduction in the amount of air plus exhaust needed is compounded by the adoption of the new XPI, high-pressure common rail injection system for 2010. Unlike unit injectors, the common-rail system provides whatever injection pressure is needed even at low rpm.

“With the rocker actuation of injectors in the past,” says Zack Ellison, Cummins’ technical director of customer support, “we had to tune the rocker lever for system performance in a way that gave less than optimum performance at low rpm” because of reduced atomization.

The result, says Ellison, is the ability to produce more torque at a lower rpm, and a more favorable torque curve, which “reduces the need to downshift.” He says peak torque is maintained down to 1,100 rather than 1,200 rpm on many of the ratings. So while Cummins has not introduced higher maximum power or torque ratings, an engine at a given rating will pull better and feel more powerful. They have, however, enhanced the number of SmartTorque ratings – 200 lb.-ft. of additional torque that shows up in the top two gears, giving drivers an incentive not to downshift.