The Ward's 10 Best Engines competition celebrates 14 years of recognizing outstanding powertrain development. In the third of our 2008 series, Ward's looks at the design philosophy behind's 2.3L DISI turbocharged DOHC I-4.
Downsizing Engine Fulfills Promise
Mazda's turbocharged 2.3L DISI engine is a harbinger of many more to come.
Picture a grinning child playing with a toy car, whisking it across a tabletop with obvious glee. “Zoom-zoom!” he exclaims.
Kids mature into adults and acquire responsibilities, jobs and kids of their own, but a fortunate few never stop having fun.
Motor Corp. has positioned itself as the car company for exactly those people. It's all about spirit, attitude and thinking young, a position that sets its products apart.
And its 2.3L DISI (Direct Injected Spark Ignition) turbocharged DOHC I-4 certainly fulfills that promise.
This marvelously muscular 4-banger reached U.S. shores in late 2005 packing 274 hp in the MazdaSpeed6 sport sedan, then expanded its grin-inspiring presence (in 263-hp form) to the quicker-still MazdaSpeed3 pocket rocket and (at 244 hp) the surprisingly zoomy CX-7 cross/utility vehicle.
The MazdaSpeed6 is gone for now, but Mazda's delightful all-aluminum DIG/Turbo I-4 — as tested in the '08 MazdaSpeed3 — is on the Ward's 10 Best Engines list for a third straight year.
Easily the strongest member of Mazda's global MZR DOHC I-4 engine family, which includes 1.4L, 1.6L, 1.8L, 2.0L and 2.3L variants in a multitude of Mazda and (part-owner)Motor Co. models in North America, Europe, Asia and elsewhere, it unleashes 114 thoroughbred horses per liter in the MazdaSpeed3 and 106 hp per liter in the CX-7.
It is engineered to optimize a ménage a trois of oft-conflicting attributes: good fuel economy, 18/26 mpg (13/9 L/100 km) in the MazdaSpeed3, low emissions and a broad, flat torque curve for powerful acceleration throughout its rev range.
While its 280 lb.-ft. (380 Nm) peak occurs at a relatively low 3,000 rpm, it offers a healthy 200 or more lb.-ft. (270 Nm) between 1,500 and 6,000 rpm. The engine's only real negative is that it requires premium-unleaded fuel despite a not unusually high 9.5:1 compression ratio.
This happy marriage of diesel-like direct (into the combustion chambers) gasoline injection and turbocharging is the technology tandem of the future to enable good performance from modest displacement, which will become increasingly important as U.S. Corporate Average Fuel Economy ramps upward to an eventual 35 mpg (7 L/100 km) in 2020.
Most OEMs look to direct injection as a lower-cost alternative to diesels and hybrid-electric vehicles.will market its version as “EcoBoost” beginning early next year with a 3.5L DIG turbocharged V-6 in the '09 Lincoln MKS sedan.
“Direct injection gives some direct efficiency benefits,” says David Coleman, lead engineer for Mazda North America's sports cars.
“The improved atomization and massive pressure drop as the fuel drops out of its 16,000-psi (1,100 bar) fuel rail pulls a lot of heat out of the combustion chamber. This improves knock resistance and allows higher compression and more advanced ignition timing, both of which improve efficiency,” Coleman says.
There also are substantial indirect benefits. For example, the higher torque allows taller gearing, which lets the engine cruise at lower rpm with less frictional and pumping losses. The turbocharger's primary contribution to efficiency is enabling a major reduction in engine size.
“If an I-4 can replace a V-6, there is a substantial savings in internal engine friction as well as in the weight of the powertrain, and the size and weight of the subframe and engine bay that hold it. The whole car gets lighter,” Coleman says.
One key challenge, especially for the MazdaSpeed3, was using engine-control techniques to help minimize torque steer.
All the basic tricks to reduce torque steer — matching length and stiffness of the axles, minimizing the scrub radius, keeping the outer CV joints in line with the steering axis — already are standard practice on most front-drive cars.
That means torque delivery had to be cautiously managed; the limited-slip differential had to be carefully tuned; and steering friction and assist had to be balanced very differently than on naturally aspirated cars.
The rate at which the turbo spools up also is different in each of the first four gears, and peak torque output is different in the first three gears, which dramatically reduces torque spikes and the resultant torque steer and wheel spin, Coleman says.
Design and engineering of the global MZR architecture was led by Mazda and co-developed with Ford.
Ford is using turbocharging and its synergy with direct injection to downsize displacement to improve economy and still deliver, or actually improve, performance vs. the larger naturally aspirated engines they will replace in its lineup.
“The beauty of this technology is that you really can do both,” says Ford Powertrain Research and Advanced Engineering Director Dan Kapp. He predicts outputs of 340 hp and 340 lb. ft. (460 Nm) from the 3.5L Ecoboost V-6 in the first application in the Lincoln MKS — as good as or better than most V-8s.
Ford plans to use EcoBoost to replace V-8s with V-6s, V-6s with large I-4s and large I-4s with small I-4s. “Obviously, CAFE has a lot to do with segmentation and mix of vehicles,” Kapp says. “But as a major part of the powertrain contribution, it will be the cornerstone of our sustainability strategy.”
EcoBoost does not carry a big up-front price tag or require any trade-off in performance.
“From a powertrain perspective, we believe this is the single biggest thing we can do — shy of diesel and hybrid, which carry a very different price tag and impact to the customer and infrastructure, because of the volume we'll realize.”
Kapp expects EcoBoost to deliver a 10%-20% efficiency improvement depending on the level of displacement downsizing. Of course, there is added cost compared with port-injected, naturally aspirated engines, but Ford says the fuel savings payback to the customer is a better value than with diesels or hybrids. The cost is further offset by the fact the engines are migrating to smaller, lower-cost architectures.
Ford also is betting direct injection and turbocharging will become more commonplace and enjoy some economies of scale.
Kapp confirms Ford's EcoBoost V-6 will expand into the 2009 Ford Flex CUV, the F-Series pickup and a wide range of global Ford vehicles following its launch in the MKS.
The technology will spread to multiple engine architectures building toward an annual volume of about 500,000 by 2012.
Many still remember an earlier round of engine downsizing and turbo boosting that followed the first fuel crisis more than three decades ago. That strategy traded low-end torque for some fuel economy improvement and introduced the dastardly duo of turbo lag and detonation knock to an American public accustomed to good low-end grunt from big displacement engines.
The major difference this time around is DIG, which (combined with variable valve timing and quicker-reacting turbos) enables higher compression ratios and better low-end torque.
How challenging is achieving the optimum balance of performance and fuel economy with a DIG/turbo engine? “Improving fuel efficiency and maintaining good performance is easy,” Mazda's Coleman says.
“Doing both at a reasonable cost is hard. The challenge is which end of that split personality to optimize and finding the performance/economy balance that people will buy.”
Coleman is not about to reveal any future product plans, but he confirms proliferating the DIG/turbocharging combo is a major element of Mazda's and Ford's fuel economy strategy.
“It's safe to say you'll be seeing a lot more DISI engines in the future,” he says. “We began discussion of the next generation rotary engine last year at the Tokyo Motor Show, and direct injection is one of the key ingredients to keeping that engine at the cutting edge of environmental technologies.”
Ward's 10 Best Engines 2008
Mazda Motor Corp.: DISI 2.3L Turbocharged DOHC I-4
Mazda Motor Corp.
DISI 2.3L Turbocharged DOHC I-4
Displacement (cc): 2,260
Block/head material: aluminum/aluminum
Bore × stroke: 87.4 × 94
Horsepower (SAE net): 263 @ 5,500 rpm
Torque: 280 lb.-ft. (380 Nm) @ 3,000 rpm
Specific output: 114 hp/L
Compression ratio: 9.5:1
Assembly site: Hiroshima, Japan
Application tested: Mazdaspeed3
EPA fuel economy, city/highway (mpg): 18/26