april2021 - 15

who were running the [Cat] C15 engine or [X15
predecessor] ISX15 engine have migrated to the
MX-13 for its efficiency as well as weight. "
The MX-13 is 400 lbs lighter than a 15L engine,
and the MX-11 drops an additional 400 lbs. This
allows a bulk material transporter, for example,
to haul more payload. The MX-11 is typically used
for regional haul, vocational, and refuse applications, while the MX-13 can be employed in those
applications as well as over-the-road and heavyhaul duty cycles.
Petroleum hauler DB Trucking in Florida specs
Kenworth T880 day cabs with the MX-11 (415 hp
and 1,550 lb-ft of torque) and 10-speed transmission.
" We don't run our engines full-tilt, " owner Dan
Marando says. " We have them dialed back to
around 400 hp. I'm a firm believer that a conservative approach creates longevity and less wear and
tear on the engines. They're also geared properly
so that they're not overrun. "
White compared the Paccar MX-13 to a " Swiss
Army knife " because of its versatility.
" A lot of times - right now more than ever -
fleets are looking at different avenues of business
to grow, and so that adaptability is very important, " he says. " The worst thing you can do is spec a
truck for one job and not be able to do any others. "
In those cases, fleets might want to spec the
more flexible powertrain.
To cater to its customers wanting flexibility,
Cummins released the 11.8L X12 in 2018 as an
option for both its regional haul and vocational
customers.
" The X12 has a higher rpm capability than many
of the existing on-highway products, but the new
design trimmed down the weight of the engine
and aftertreatment by 650 lbs, which makes it now
the lightest engine over 10L on the market, " says
Kris Ptasznik, Cummins product manager for the
heavy duty on-highway segment. " The low-friction
design also reduced parasitic losses for a 6 percent
bump in fuel economy. "
Ptasznik adds that a Cummins X12 or X15
engine integrated with an Eaton Endurant
transmission can " offer the lowest total cost of
ownership and greatest maintenance intervals, so
equipment can stay on the road making money.
When it is an option, customers should look
beyond the sticker price and instead focus on
cost over time. "
The U.S. Environmental Protection Agency's
Greenhouse Gas Emissions Phase 2-compliant
2021 X15 Efficiency Series was designed for
75,000-mile oil drain intervals for trucks averaging 7-plus mpg. Through the Cummins Oil-Guard
oil analysis program, that can be pushed to
100,000 miles.
That integrated powertrain also can boost
safety. All X-Series now offer drivability features
including onramp boost, predictive engine braking, predictive gearshift, and dynamic power.
Along with the X15, Navistar International
LT Series customers can also choose the A26
Big Bore engine, which the OEM launched in
2017. The 12.4L engine ranges from 365-500 hp
and provides a more modest option that weighs
2,299 lbs, which is 27 percent less than the X15
Productivity Series and 22 percent less than the
Efficiency Series.

Less is more

After finding the optimal displacement, the next
thing to figure out are the proper horsepower and
torque ratings. According to Johan Agebrand,
director of product marketing at Volvo Trucks, the
" sweet spot " is roughly 400 to 425 hp for trucks
with a 70,000- to 80,000-lb GVWR and 1,750 lb-ft
of peak torque.
Geography matters, however, Agebrand
explains. If fleets run more in the flatter Midwest,
400 hp is sufficient, while along the rougher
terrain of the Northeast or Rockies, 455 hp would
be a better rating. A dump truck that constantly
climbs out of steeply graded gravel pits would
need 500 hp, though, Agebrand said.
" It's going to come down to really understanding
your route and where you are going to run, and
then the OEM can help you with what that means, "
he adds, advising not to over- or underestimate.
Automatic manual transmissions have also
helped push horsepower requirements down.
" AMTs have changed how we can design the
engine, " Agebrand explains. " The engine doesn't
need to be really heavy on torque or horsepower in
the high rpm range anymore;
the only occasion we drive
there is while going downhill,
when you will rev it up a little
bit to get the most engine braking power you can get. "
When spec'ing, Agebrand
advises to not overestimate
how much power is needed.
He said while fleets may often
spec 425 hp, that much power
could be excessive and that " a
lot of people could live with
405 hp. " It does truly depend
on the application, though.
A flatbed operation would
still require 455 hp, as it
cannot employ friction-reducing technology such as trailer aero kits and needs that
extra power.
One trend the adoption of
AMTs allowed for is downspeeding. This refers to the
speeding up of the rear gear
ratio to lower the engine speed,
allowing the engine to achieve
a truck's most efficient rpm
with the lowest horsepower to
maintain a cruise speed of 65
mph. According to the North
American Council for Freight
Efficiency, downspeeding can
cut a truck's fuel cost by up to
3 percent.
Agebrand says except for
the D11, all of Volvo Trucks'
diesel engines are downsped.
The D13TC (turbo compound)
engine, launched in 2017 and
updated in 2020, has taken
advantage of this technology,
improving fuel efficiency by
11 percent versus 2015 model
year trucks.

»To see if the Volvo D13TC is the right fit economically
for a fleet, Volvo offers an online spec'ing tool
called the Turbo Compounding Calculator that
factors in rear axle ratio, fuel and diesel exhaust
fluid prices, and miles traveled per year.
Photo courtesy of Volvo Trucks North America

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April 2021 | FleetMaintenance.com

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