The 13-liter acquitted itself well, giving smooth torque delivery and responding promptly to the throttle in the way we have come to expect from engines with variable geometry turbocharging. One thing that was apparent was the sensitivity of the foot feed. Any pressure on the pedal – even just a brush of the foot – would bring up the rpms. As a result, a conscious effort to remove any pressure had to be made when easing up through the gears.
The engine was impressively quiet. Multiple injection events to cut NOx from the engine also serve to significantly reduce diesel knock, and with its particulate filter damping out exhaust pulses, there was no exhaust bark to this Bulldog. There was no trace of the timing gear noise at idle I had noted on the prototype Pinnacle I drove a year ago. I had deliberately looked for any noise because the timing gears are at the rear of the engine. On this production Pinnacle, the bulkhead and doors are impressively sealed. The idle noise was just 59 decibels, with the engine making very little contribution to the overall noise at a 60-mph cruise. Here I recorded 75 dB(A) rising only to 76 at the full power test (45mph at 75 percent rated engine speed). And using the very effective engine brake – the PowerLeash – brought little noise, again thanks to the DPF.
As noted with previous Macks, the ride and handling were good, especially considering the state of much of the highway we encountered. One wonders what Pennsylvania does with the money it collects in fuel taxes – a lot more of it could go to highway maintenance. A particularly noteworthy aspect of the suspension is that there are no surprises as the truck leans into the corners; the right amount of steering is easy to apply and no correction is needed. It did take a day to get used to the steering in the straight ahead position – I was sawing at the wheel initially, but by the second day I noticed considerable less activity at the wheel.
Day two was a far different drive, southwest toward Hagerstown where the hills start to flatten out so we could shoot for fuel mileage. Taking fuel information from the driver display, I had found the fuel mileage in the more performance-oriented drive of the day before was 5.2 mpg returning to Allentown after nearly 300 miles. Zeroing the trip and driving for economy – mostly holding 58-60 mph and using the cruise sparingly – I managed to get the fuel mileage up to 5.9 mpg on the interstates. It fell back to 5.8 after negotiating the local streets back into the Mack parking lot.
Of course, this particular truck was spec'd without fairings – not even little cab extenders – and the dry van trailer was also without any Nosecone or similar aids. That can seriously impact fuel consumption, maybe as much as a half mpg. In light of this, the fuel mileage doesn't look bad.
McKenna says the new engines are as good as or better than the ASET E7 engines they replace and was hoping for the low- to mid-sixes or better. He was a bit baffled but thought the cause might lie in the DPF as well as the lack of fairings. The tea-kettle design – known as the Mack Cap – has an annular passage through which the exhaust passes to reach the ceramic filter. It seems that many of the earlier deliveries of the devices have a too-tight clearance. When this happens, the exhaust backpressure rises and the system does not fully regenerate, leading to some loss of performance and to poorer fuel economy. It may be the case here.
The excellent driver display has been noted. It's worth returning to it, because the screens available are very well-designed to give the driver, technician and owner all the information very simply and intuitively. I had assumed, because the control stalk was the same as Volvo's, that the rest of the system would be the same, but it is entirely a different interface and much easier to use than Volvo's.
Another factor that will appeal to the driver – at least on this truck – was the back of cab access via the storage boxes. I was surprised the cab access was not as convenient, lacking a low-mounted grab handle at the hinge side of the door opening.
The engine access is good, even with the added complexity of today's EGR systems. In fact, the new engines are considerable cleaner, externally, than the earlier E7, with components that might need service easily accessible.
A nice feature of the Volvo/Mack EGR is a "short-circuit" in the plumbing that returns exhaust gas back to the turbo to raise the temperature of the exhaust and aid in the active regeneration process. Mack, like Volvo, also uses the VG turbo to raise exhaust backpressure during start-up to get the engine up to working temperature faster.
The phrase "Built Like a Mack Truck" has passed into the language. There's no denying the Mack is a tough truck. The refinements to the cab make it very durable, and in over-the-road applications with new chassis and cab upgrades, there can be no doubt that Mack's enviable reputation for toughness will ensure a long life.
Now that the troubles of the E7 engine are a thing of the past, the reliability that was lacking in the last few years has been addressed. McKenna proudly pointed out that, even as new as the engines are, they are much, much more reliable than the E7 at the end of its development.
Mack products – because they have such a high Mack content – possess an individual character. And despite the commonality of some components with its sister division, the distinctiveness that spells Mack is patently displayed in the Pinnacle. To the driver, it means a particular style, particular driveability, particular performance and particular durability.
And with its legendary durability on track, the Bulldog is back on the Pinnacle with the MP-8.