Volvo Trucks now offers a 455-hp rating for the XE13 – standing for "exceptional efficiency" – powertrain package that links the D13 engine and iShift transmission with special programming. The initial XE13 package with a 425-hp rating was launched last fall. The new version adds horsepower while still allowing the engine to cruise down at 1150 rpm at 65 mph.

The XE13 concept first focused on fuel-conscious fleets with trucks that spend considerable time cruising at highway speeds, the company says, while the new rating is aimed toward the higher performance demands of long-haul fleets.

This lowering of engine rpm at a given vehicle speed is a concept Volvo calls “downspeeding”.

The company says customer data shows that the XE13 package consistently operates between 1050 and 1500 rpm, with up to 70% of operation in the most efficient range of 1100 to 1200 rpm. You gain about a 1.5% fuel-efficiency improvement for every 100 rpm of downspeeding, says Volvo, so the 455-hp XE13 package should deliver about a 3% gain, sane as the earlier version.

The package, available on Volvo VN series tractors, is rated for gross weights up to 80,000 lb and includes: Volvo D13 455 engine with 1750 lb ft of torque; Volvo I-Shift overdrive transmission with a 0.78:1 ratio; and axle ratios of 2.64 to 2.69.