Mack’s 13-liter MaxiCruise on-highway engine makes the sweet spot even sweeter.

When Mack unveiled its MaxiDyne engine in 1965, it challenged the standard premise that diesels run best close to the top of the engine’s rpm range. The engine operated in a range from 1,050 to 2,100 rpm and produced almost as much power running at 1,050 as it did at 2,100.

“That was so-called constant engine power,” says David McKenna, Mack’s director of powertrain sales and marketing, and it was achieved via “a broad expanse of torque at the bottom end.” Where torque tapered, horsepower picked up the slack.

Mack’s modern on-highway MaxiCruise, the 13-liter MP8, operates on a similar notion, though executed slightly differently. “Customers always look for that bottom-end grunt that Mack engines offer,” McKenna says. “We had to maintain that.”

Where it distinguishes itself from its predecessors, though, is in its horsepower offerings relative to the engine’s rpm level. McKenna says Mack dubbed the MP8 a “hump horsepower engine,” meaning it offers more horsepower when running at cruise speed than at higher rpm levels.

“At 1,400 rpm, you could conceivably have 505 hp, yet at 1,800 rpm, you might be down to 420,” he says. “It encourages drivers to operate closer to what benefits them. It offers them a lot of power in and around the sweet spot.”