The EPA27 VGT engine brings increased horsepower and improved braking performance to an industry workhorse

As a leader in the industry, Mack Trucks has accepted a heightened responsibility to clean energy. With the new Granite®, Mack saw the opportunity to task its design team with a challenge and outfitted the Granite with the 13-liter f. By doing so, the Granite has capitalized on an improved level of horsepower and enhanced braking.

Morphing from the Existing VGT to the All-New EPA27 VGT

According to Kevin West, Senior Product Manager for Vehicle Propulsion at Mack, the new VGT’s improvements are based on an enhanced quality perspective. A high pressure fuel pump has been added to the new power source and has increased cylinder pressure. With the compressed graphite block, the Granite surpasses performance expectations while reducing emissions.

“With the new VGT, we have a higher compression ratio,” says West. “We go to a 20:1 compression ratio now and have a new turbocharger that improves efficiency and responsiveness.” The turbocharger’s redesign creates impressive gains, including increased efficiency.

“With the ball bearing wastegate and optimized veins for improved airflow, the goal is targeted at improving efficiency and of course the responsiveness the driver gets out of the engine,” says West.

The improved VGT comes equipped with a seven-wave piston bowl that has added dividers between the initial waves to create more collisions, ultimately achieving better fuel atomization.

“Effectively, you’re trying to accelerate the fuel mixture to attain a faster, more complete burn,” says West. “In doing so, we get better fuel mixture, lowering engine outlet CO2 and reducing soot and particulate matter.”

The boost in power is evident in the Granite’s ability to provide up to a new 540 horsepower rating, while maintaining the torque rating at 1,950 pound-foot, according to West.

Paired with the shifting improvements rooted in the updated mDRIVE transmission, the improved low-end torque of the VGT will solidify an enhanced driving experience.

“You can still run it and rip it up through and get to where you’re at the higher horsepower and the higher revolutions, but what you’re going to be able to do with the Granite is you’re going to be able to lug it longer and down to a lower rpm than what you were able to do before and maintain a gear longer than you would have previously,” says West.

Operating the New Granite

‘Smart operation’ describes the intended use of the vehicle and the best way to operate it. The new Granite is outfitted with an mDRIVE that ensures ease in shifting with an emphasis on down shifting action to ensure maximum engine braking power.

“We continue to strive to make the mDRIVE shifts as seamless as possible,” says West. That shifting ease comes from a faster communication link between the transmission and the engine itself. The faster they communicate, the faster they can synchronize speeds, and the faster that shifting sequence can occur.

“We reworked the valves in the transmission control module to improve overall shifting speed and responsiveness,” says West. The new Granite’s transmission includes an additional customer-focused enhancement with its creeping mode feature allowing the transmission to walk slowly forward without the operator having to actually apply force or pressure to the throttle pedal.

“When this feature is engaged, you can let your foot off the brake and the truck will start to creep forward,” says West. “It's going to slowly start to engage the clutch and move the vehicle forward at idle speed.”  West adds, “I can’t tell you how impressed I was to experience the truck walking up a 22 percent grade with a load of stone, just by taking my foot off the brake with the feature engaged.”

The Granite’s creeping feature allows for improved performance through better maneuverability. Low speed engaging work is smoother and easier with an ability to reduce lugging and lurching in low gear.

With enhanced maneuvering and capability, it was only fitting the new Granite’s stopping power improved, too. In true Mack spirit, the Granite’s engine braking system was upgraded, as well.

West points to improved engine braking performance of over 20 percent as another dominating improvement. Operators can see a maximum of over 630 braking horsepower, accomplished with a pre-turbine throttle. That comes in as a significant increase compared to the previous 505 braking horsepower rating.

“When you’re in a loaded dump truck going down a 30 percent grade and it just walks you down, its impressive,” says West. “I believe it is one of the best engine brakes we’ve ever had.”

While improving upon a product like the legacy Granite is an unenviable challenge, Mack explored every opportunity for improvement. Focusing on meeting EPA27 emissions standards, Mack’s design team was able to take a truck with a superior reputation and legendary working ability and elevate it further. With an upscaling in power and performance, the new Mack Granite has positioned itself as the premium choice in the vocational market.

The all-new Mack Granite will also offer the Cummins X10 engine (350-450 horsepower, 1250-1650 lb-ft torque) with the Allison 3000/ 4000 Series Transmissions.