Talk about cross-border shopping.
International shopped around the world looking for a partner in the big-bore engine that would become the MaxxForce 11 and 13. The company knew it didn’t have the scale to engineer and build a cost-effective, high-performance engine, so it went looking for a partner that had a great product and wouldn’t be competing in North America.
The result was a joint development agreement between International and Germany’s MAN Nutzfahrzeuge. Overseas, the engine is called the MAN D20. More than 200,000 of them are in currently in service.
The North American version of the engine features the same basic infrastructure as its European counterpart (block, crank, head, etc.), but with electronics, and fuel and air management systems engineered to meet North American emissions standards and customer expectations.
The engine block is interesting in its own right. It’s made of compacted graphite iron (CGI), which International claims is 70-percent stronger and 40-percent stiffer -- with double the fatigue limit -- than traditional cast iron. CGI is a precision casting process where a small amount of magnesium is added to the molten iron. The resulting increased stiffness and strength allow for a lighter casting. At 2,244 lb, it’s 300 lb lighter than Cat’s current C13.
A series of vaulted panels on the side of the block is designed to minimize noise, and the result is quite amazing. That, along with several other noise-reduction strategies make MaxxForce a very quiet engine.
Air and Fuel Control
While quiet won’t get you down the road, MaxxForce’s solid low-end torque will. While the engine has a European heritage, the make-it-go stuff is tailored to meet North American requirements and expectations. Having said that, engineers have given the engine a distinctly European personality because, well, because it works.
Full torque output is available at 1,000 rpm, with more than 80 percent of that available at clutch engagement. Drivers will find high torque at low engine speed an economical way to operate.
“The key to combining fuel economy and performance is to bring engine speed down. There’s a lot more internal friction at high engine speed, but on the low end, you have less friction and parasitic loss as well as full torque, making the engine very drivable,” says Helmut Endres, International Truck and Engine Corp.’s VP of engine and product development. “We really have to convince our customers to adapt to the new, European torque curves of this engine.”
Several fleet representatives were present at the MaxxForce product launch in Las Vegas a couple of months ago discussing their experiences thus far with the product. Ray Williams of Estes Express Lines of Richmond, VA told us he had to break with tradition an spec an overdrive transmission to get the engine revs down.
Estes has been running 300 hp Cummins ISMs with direct transmissions. That spec had the 11-litre MaxxForce wound all the way up to 1800 rpm at 60 mph, which is way outside the optimum cruise speed. They let it go for a few months, and saw fuel mileage in the 5.3-5.4 range. After switching to an 0.78 overdrive transmission and getting the revs down to 1,300, fuel economy improved to 6.27 -- nearly a mile-per-gallon difference.
“Those engines don’t like to run fast,” Williams says. “We’ve got them down to 1,300 at 60 mph and the drivers say they pull just fine. Now we’ve gotta get them used to driving a low revving engine. That’ll be a job for our driver trainers”
To achieve good performance at low rpms, MaxxForce has combined dual-stage turbocharging with high injection pressures and optimized intake air temperatures.
There are two turbos on the engine, operating in series, but independently of each other. Each are “simple” turbos, i.e., not variable geometry designs. The primary has a small compressor wheel which spools up very quickly to provide adequate volumes of air in lower gears when power demand is modest. The secondary turbo, while allowing the free movement of air through it from the primary turbo, is larger and capable of moving larger volumes of air when power demand is higher, like at cruise speed and when climbing hills.
“On a single stage system, a larger turbo might be spinning at 20,000 rpm at low engine speed, whereas with the smaller first stage turbo in this system, we get speeds of 60,000 rpm, making the turbo much more responsive,” Endres points out. “Turbo speed is what gives you boost (higher intake manifold pressure).”
One of the unpleasant offshoots of EPA’s emissions restrictions was fairly poor transient performance, especially when downshifting or climbing hills. The driver would feel a lag after the shift before the power came back because the system was programmed to not deliver substantial amounts of fuel until it had the airflow from the turbo to support the proper fuel-to-air ratio. Otherwise, you get a lot of smoke.
MaxxForce’s smaller fast-spooling primary turbo delivers enough air quickly, so more fuel can be fed to the injectors, and that gives the engine very quick throttle response.
Fueling is managed by a Bosch 26,000-psi common rail fuel injection system. There’s constant high pressure at the injector even at low engine speeds, and MaxxForce engines use an injector with carefully engineered hole configurations that’s said to be 85 percent efficient. The fuel injection system is also capable of multiple injections per combustion event, which yields a more complete, more efficient burn, with less noise.
The last piece of MaxxForce’s combustion optimization strategy is carefully controlled intake air temperature. MaxxForce uses two water-cooled air intercoolers in series after each turbocharger. There is no charge-air cooler on this engine.
As a result, air intake air temps can be kept very close to ambient temperature, International says. That’s good for the fuel-to-air ratio, good for efficiency, and good for drivability.
But Does it Work?
I recently tested an International TransStar (formerly known as the 8600 model) equipped with the 13-litre version, rated at 410 hp / 1,450 lb ft, running a trip from Chicago’s western suburbs over to Fort Wayne, Ind. I grossed 66,000 lb under a flatdeck loaded with concrete Jersey barriers.
Winding my way from International’s Melrose Park facility out the freeway gave me a taste of some city driving. There’s pull under the pedal right from clutch engagement, and hitting peak torque at a mere 1,000 rpm means there’s absolutely no need to take the revs much higher than that on the bottom side of the gearbox.
At highway speeds of 60 mph (1,300 rpm), I applied a little trailer brake a few times (there are no hills between Chicago and Fort Wayne) just to get a sense of the engine’s pull and it was respectable. Even down at 900 rpm under load, it pulled solidly.
Since fuel economy is best at lower engine speeds, MaxxForce has a broad enough torque band to cruise at 1,300-1,400 rpm with more than a little in reserve for the hills. Peak torque sits between 1,000 and 1,200 rpm.
The lack of engine noise made for a pleasant drive, too. I drove a MaxxForce equipped ProStar a few weeks earlier at a product launch event in Las Vegas, and while it was much quieter than the TransStar day cab, I have to give the TransStar/MaxxForce combination very high marks for sound attenuation.
While in Las Vegas, journalists had a chance to talk with the fleets guys who are doing reliability testing with the MaxxForce engines, and a couple of them reported fuel economy numbers in the high sixes (US), which isn’t bad for engines with less than 50,000 miles on them.
My first impressions of the MaxxForce engine are good. It may be new to North America, but it’s got a good track record in Europe. It’s light and torquey, and more than able to move typical linehaul or regional loads efficiently. If your operation doesn’t demand a big block engine, MaxxForce is worthy of consideration.