Under Control: Mack Pinnacle with mDRIVE

By on November 2, 2012
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You may have seen one of those cable TV shows geared for motor-heads (pun intended), where a hot rod shop, customizer or a restoration specialist takes someone’s car and rebuilds it, incorporating all the latest features. My favorite episode of one of those shows was when they took a 1950s pickup truck and smoothed out the body work, then put a brand new crate motor and modern transmission under the truck. Not only did it look modern, it ran better than anything available in showrooms.

What Mack did to the Pinnacle reminded me of that episode. In 2007, the then-new Pinnacle was designed to help Mack penetrate the on-highway segment of the heavy truck market.

In the ensuing five years, competitors improved their aerodynamics, and technical development shifted from meeting the 2007 and 2010 EPA emissions regulations to improving fuel economy and drivability. The culmination of Mack’s efforts is the Pinnacle SE featuring the Super Econodyne package.

Econodyne was the name given to Mack’s 12 -liter engines back in the 1960s. The competition was running 14 and 15 liters. The only other 12-liter was a two-stroke. Mack knew then that torque, not horsepower, moved loads, and they offered maximum torque at lower engine speeds. When other engines needed to run faster than 1,800 rpm or risk lugging, Macks ran at 1,500 rpm and below.

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What’s new

The Super Econodyne package is engineered to lower engine operating speeds more than 200 rpm from today’s speeds, according to Dave McKenna, director of power train sales and marketing at Mack Trucks. It consists of the MP8-445 SE engine mated to Mack’s mDRIVE automated manual transmission and proprietary C125 drive axles. The new axles alone are reported to improve fuel economy 1.5 percent.

With the old Econodyne package, the engine’s operating range was 1,200 to 1,500 rpm with a 3.25 to 1 drive ratio. The Super Econodyne drive ratio is 2.66 to 1, and improvements give it a useful operating range from 1050 to 1500 rpm. Both packages use a 0.78 overdrive ratio.

The old Econodyne ran 65 mph at 1,380 rpm. The new Super Econodyne cruises at 65 mph showing just 1,160 rpm on the tach. Much of the improved drivability of the package has to do with the mDRIVE transmission. It almost feels as if it’s programmed to anticipate the driver’s needs.

The sweet spot

Driver differences are the greatest contributors to fuel efficiency, and that’s where the mDRIVE helps. It provides optimum shifting for all input conditions, due to the way the engine and transmission communicate. “There is a great deal of proprietary information in the operation of a modern electronic engine,” McKenna says, “especially fuel mapping.” That’s the complex formula that the computer uses to evaluate how much fuel is needed for different load demands and operating conditions. The computers then determine the fuel’s precise timing through the injectors.

The mDRIVE transmission uses that data to determine the optimal gear to be in and the ideal shift points for all operating conditions. The MP8-445 SE and the mDRIVE communicate continuously. That’s what makes them so effective together. By themselves, they account for about a 2 percent improvement compared to a 10-speed transmission.

The mDRIVE has 28 percent steps between gears, compared with 38 percent with 10-speeds. That allows the Mack gearbox to stay closer to the engine’s sweet spot, where fuel consumption is at its lowest per unit of power produced. Splitter transmissions (13-speed and 18-speed) with 18 percent steps stay closer to the sweet spot but add complexity and depend even more on driver input.

Mating the engine and transmission integrates the drive train to improve fuel economy and performance but still react to power demand expressed through the driver’s right foot. No matter how you drive, the MP8-445 SE and mDRIVE will work together to squeeze the most out of every drop of diesel.

In the driver’s seat

So much for the theory of why it works. I was eager to determine how it works. Mack had several Super Econodyne models ready to put theory to practice on their test and demonstration track. The track is about three quarters of a mile around with 12, 15 and 20 percent grades in it.

The last truck I drove there was a Pinnacle with Mack’s MP8-505 and a 10-speed. Both then and now, I approached the steepest grade in cruise control to see how long the truck would hold speed before I had to shift. At 20 vertical feet for every 100 horizontal feet, the grade compressed time, and even with 505 hp I soon had to shift.

The 445 and its mDRIVE transmission surprised me. Speed came down quickly as expected, but the transmission took over and made some very smooth downshifts. It has a grade sensor inside, so it even skip-shifted down. Although both power plants put out 1,760 pounds-feet of torque, the 445 hp 13-liter actually outperformed the higher powered one going up the hill, even from a standing start.

Off the track, the Pinnacle handled the Pennsylvania roads smoothly. The occasional bump and a set of railroad tracks tested the suspension with no difficulty. Visibility was among the best of modern trucks, with a sloping hood and large side windows that kept each side mirror, including the lower, convex section, completely in view at all times. I wish I had time to do a longer drive, to experience more varied road conditions and to get a more realistic sense of the Super Econodyne’s fuel economy. Drag racing up a 20 percent grade can throw the readout’s mpg reading way off.

On my last test drive, I praised the Pinnacle’s ride, comfort, ergonomics, performance and quiet. The new version is even better. Just like the TV shows, Mack made small improvements to the body and chassis and a major improvement to the drive train. The result is all that Mack planned for.

About Paul Abelson

Paul Abelson is the Senior Technical Editor of Road King magazine.

One Comment

  1. Hector Muñoz

    November 30, 2012 at 10:17 pm

    excelente diseño

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