New engine technology promises not only improved engine efficiency, but also the ability to spec your drivetrain to further enhance fuel economy.

Exhaust gas recirculation creates higher exhaust backpressure and slower combustion in the cylinders, which reduces fuel economy. How can the situation be remedied?

One answer is proving to be selective catalytic reduction. SCR technology in 2010-2011 engines has a beneficial side effect: It allows engineers to reduce EGR levels by retuning engine parameters. This yields an often-overlooked side benefit – an enhanced ability to produce power and torque. By smartly spec’ing your transmission and drive axles to give a lower cruise rpm, you can take advantage of engines that pull better, and can increase fuel economy even beyond the gains produced by the retuning.

Don’t underestimate the value of low rpm cruising. The most efficient diesels are the slow-turning, ocean-going ship engines. Some turn at only a tenth of the rpm of a modern truck diesel.

“We’re selling torque, not horsepower,” says Ed Saxman, product marketing manager for Volvo. He points to Volvo’s 13-liter engine, which produces 500 hp and 1,750 lb.-ft. of torque, as an example.

For Detroit Diesel’s DD15, “The torque lasts down to 1,000 rpm,” says Chuck Blake, Detroit Diesel’s senior technical sales support manager. The company’s amplified common rail system produces maximum injection pressure at these lower rpms, which smoothes out low rpm combustion and enhances torque. In addition, the camshaft no longer has the job of operating unit injectors, and is driven by the rear end of the crankshaft where the flywheel is. These changes mean much less vibration produced by the engine’s mechanical parts. As a result, “It won’t miss a beat at that rpm,” Blake says.