The latest version of Mack’s 13-litre workhorse will cause a lot of operators to rethink their need for big-block power. The MP8 505C+ now cranks out 505 horsepower, but more significantly, a whopping 1,860 lb-ft of torque. That’s right up there with the big-block 15- and 16-litre engines.

Better still the 505C+ delivers all that power in every gear, producing peak torque across a range from 1,100 to 1,400 rpm and peak horsepower from 1,400 to 1,750 rpm. That means there’s hardly any need to ever take the engine much beyond 1,700 rpm or so. In fact, much of the time at cruise speed will be spent at a very efficient 1,400 rpm or so.

Ultimate Test Drive recently spent a day in an axle-forward Pinnacle pulling a fully loaded Super B-train around the Nanaimo area on British Columbia’s Vancouver Island. At 138,800 pounds gross combination weight, the MP8 got a good workout and it proved itself very capable with the big weight.

While 13-litre engines pulling big Super-B loads may come as a surprise to some, we are aware of several fleets doing just that. And they have been doing it for a few years now.  I was a little skeptical when I first about the practice, but Mack’s Director Technical Sales Support, Dave McKenna reminded me that horsepower is horsepower and torque is torque, regardless of what size 
engine it comes from. Irrefutable logic, of course, but being a stubborn old gear-jammer, I had to see for myself.

While larger-displacement engines will usually produce more power, this 13-litre engine is right up there with the best of them. Mack says a combination of tweaks to the engine software, including adjusted timing, and highly tuned fuel injection events, are responsible for the higher output. The advantage is you get an engine fully capable of delivering almost as much power as the largest engines available today in a significantly lighter package.  And at 505 horsepower and 1,860 lb-ft, it’s more than enough to handle a loaded Super-B in this demanding environment.

The truck we drove also had an mDRIVE automated manual transmission with the optional Premium Shift Pad. That allows drivers to manually switch the transmission shifting parameters between what Mack calls Performance and Economy modes. Thanks to the high level of integration between the engine and transmission, the transmission is programmed to seek the most economical shift points under the circumstances, taking into account grade, weight, and to some extent driver demand.

After a full day with the truck, I’m pleased to say I’m no longer a skeptic. This 13-litre is certainly up to the Super-B challenge. While shooting the video we made several runs over a 10-mile course and 
compared the two modes in the same sections of road. There was a difference between Performance and Economy modes, and for the driver the choice would be a no-brainer. But for the person paying for the fuel, the difference between the two was, in my mind, enough to make you think before pressing the PERF button. Sure it rolled the power on more assertively and revved a little higher, but at what cost?

If getting to the top of the hill first is top of your list of priorities, you’ll lean toward the 15- and 16-litre engines, so don’t waste your time with this. But if you don’t mind taking a few minutes longer on a really long grade and you love the smell of money more than diesel exhaust, this might be your next engine.