Pinnacle of Performance

Steve Sturgess | June 01, 2012


Powering the Pinnacle

The MP8 is the 13-liter engine in Mack’s lineup, which also includes the MP7 and MP10. The numbers derive from the displacements stated in cubic inches. So the MP7 (11-liter) is actually about 670 cubic inches, the MP8 is 790 cubic inches and the MP10 (16-liter) is 970 cubic inches.

All are single overhead camshaft engines with the camshaft drive at the rear of the cylinder block. This allows the fluctuating loads from the injector lobes on the camshaft to feed directly into the flywheel rather than along the length of the crankshaft, thereby reducing torsion in the engine and improving injection timing performance.

The MP8 at the 505-horsepower rating has a power density of 38.8 hp per liter. At this rating, then, the engine is several hundred pounds lighter than similarly rated 15-liter engines. Torque rating is 1,760 lb.-ft.

All MP engines are available in three engine families: Econodyne, MaxiCruise and Maxidyne.

The Econodyne personality is mapped for typical interstate applications with extended times at engine cruise speed — part-load, part-throttle applications where fuel economy is a priority. The MP8 in the Pinnacle I used in the drive test is an Econodyne and is very much the highway tractor.

The MaxiCruise engines perform best on rolling interstates in on- and off-road applications and are well-suited to vocational applications. Maxidyne engines provide high power for low-speed, high-performance and severe-duty conditions, especially off-road.

Econodynes use an intelligent torque management strategy called EconoBoost to provide extra muscle to keep vehicle speed constant under full engine loads and to avoid downshifts. Initiating at 1,300 rpm with the driver maintaining speed for three seconds of full throttle (while in the top two gears), EconoBoost provides up to an additional 200 lb.-ft. of torque for as long as needed, allowing the engine to stay in a higher gear to crest a hill or make a safe pass.

Backing up the MP8 engine is the mDrive transmission available exclusively in the Pinnacle. It’s a 12-speed, two-pedal automated mechanical transmission with a base torque input capacity of 1,920 lb.-ft. The mDrive is designed to integrate seamlessly with the MP7 and MP8 engines, and the gearshift is operated by an intelligent shift pad. The mDrive continuously monitors changes in grade (both up and down), vehicle speed, throttle position, acceleration, torque demand and combined vehicle weight.


Mack Pinnacle Axle-Back test vehicle specs

Frame: Mack, 266-by-90-by-8 mm

Engine: Mack MP8 505C 13-liter, 505 hp, 1,760 lb.-ft. torque

Engine brake: Mack Powerleash

Transmission: Mack mDrive tMD 12AO automated mechanical 12-speed overdrive

Wheelbase: 233 inches

Front axle: 12,000-pound dual taper-leaf suspension

Front tires: Bridgestone R280F, 295/75R22.5

Rear axle: Mack S40C, 40,000 pounds, 3.25:1 ratio

Suspension: Mack 40,000-pound air-ride

Rear tires: Bridgestone M726 EL, 295/75R22.5

Wheels: Alcoa 8.25-by-22.5 hub pilot, outside polished

Fuel tanks: Dual 140 gallons polished

DEF tank: 23 gallons

Fifth wheel: Fontaine air slide

Seats: Mack proprietary UltraLeather

Interior: Grand Touring

Other: Mack 70-inch mid-rise sleeper; roof fairing, skirts, side extenders; exterior sun visor; heated, motorized mirrors; remote keyless entry; AM/FM/CD weatherband radio w/ iPod interface; automatic temperature control HVAC; daytime running lights; 160-amp alternator; Borg Warner on/off fan clutch; gear reduction starter; Davco 482 fuel/water separator

More About: strives to maintain an open forum for reader opinions. Click here to read our comment policy.