Say you have a perfectly fine 2.0L direct-injection gasoline turbocharged 4-cyl. that puts out 200 hp and 207 lb.-ft. (281 Nm) of torque, has good fuel efficiency and won three straight Ward's 10 Best Engines awards. Then you decide to design a new and better version.
Do you, like many auto makers, base it on the old one and share as many parts as possible? Do you bump its displacement to increase output, just to make sure everyone knows it is a new engine?
Not if you're Audi AG.
This latest-generation EA-888 2.0L TFSI I-4 powers Audi's '10 A4 sedan and Avant wagon, A5 coupe and Q5 cross/utility vehicle, as well as the '11 TT sports car.
It delivers 211 eager horses and a hefty 258 lb.-ft. (350 Nm) of torque and shares virtually nothing except cylinder spacing with its same-displacement predecessor, which still is seeing duty in the A3, TTS and a variety of other Volkswagen AG products.
“The EA-888 was practically a new engine by the time they were done with it,” says Audi of America Inc. (A3, A4 and A5) Product Manager Carter Balkcom.
“They wanted to do so many things to optimize it for efficiency that everything from the block to the intake manifold to the turbocharger to the valvetrain was redesigned.”
The engine's most significant new hardware is a 2-stage variable-lift AVS (Audi Valve System) on the exhaust side. Originally launched on the intake side of Audi's 3.2L V-6, the 888 I-4's exhaust AVS is largely responsible for this engine's impressive torque output, which reaches its peak at just 1,500 rpm and stays flat well beyond 4,000 rpm, Balkcom says.
And, as in most modern engines, the intake valves benefit from efficiency-enhancing variable timing.
“There's not much benefit to variable lift on the intake side of turbocharged engines, but we use it for both power and efficiency on the exhaust side of the 888,” Balkcom says.
“If you were to try to tune this engine for this kind of torque performance without AVS, it would not run very smoothly. You would have a lot of residual exhaust gases in the cylinders and cross-talk between them as you try to expel them. The 2-stage lift allows us to purge residual gases out of the cylinders in a quick and efficient way.”
The mechanism is relatively simple. Each exhaust cam lobe is split into two halves with different profiles, and two electrical solenoids operate a plunger that rides in a runner on the camshaft.
When the engine computer decides it's time to change profiles, “it sticks a finger into the runner, causing it to laterally shift. When it's time to shift back, a second finger goes into a different groove and moves the shaft the other way,” Balkcom says. “It's a technology that we developed in-house, and we make all of the parts in-house.”
The entire turbocharger assembly also is redesigned. “Everything from the impeller vanes to the way it mounts on the manifold,” Balkcom says.
“The waste gate and impeller are new designs, and the turbo's positioning on the manifold is revised, all to optimize the flow of exhaust gas going through the exhaust side of the turbocharger and compressed air coming into the intake manifold.” The overall efficiency improvement is about 6%.
Among this engine's other advancements is significantly lower internal friction.
“The cylinder bores have a new type of finish that allows us to use lower piston ring loads without increasing oil consumption. New-design crank bearings have a low-friction lacquer coating, and a new oil delivery system has a variable-pressure oil pump that delivers lower pressure when the engine doesn't need higher pressure but ramps up to higher pressure when it does,” Balkcom says.
Dean Tomazic, engine performance and emissions vice president at powertrain engineering specialist, FEV Inc., calls it “remarkable” that this turbocharged DI 4-cyl. meets federal Tier 2, Bin 2 and California super ultra-low emissions vehicle (SULEV) levels.
Tomazic says the engine's low-emissions recipe includes a single-scroll turbocharger.
“Many turbocharged gasoline engines have twin scrolls, which have some advantages, but the single scroll can handle higher temperatures and is good for cold start (emissions),” he says.
“The single scroll has less thermal losses because there is no inner wall, so the cool-down effect of the exhaust during cold start is significantly lower, and back-pressure is lower. From an efficiency and thermal management perspective, that is a big advantage.”
The second prime ingredient, Tomazic adds, is the exhaust-cam AVS. “The short cam, which has a 180 degree event and is used up to 3,000 rpm, allows (engine designers) to basically separate the four cylinders from each other to avoid backflow of exhaust.
“The intake ports have a little ‘drumble’ — a mixture of tumble and swirl — that gives very stable combustion and extreme spark reservation during cold start,” Tomazic says.
“You need stable combustion and late combustion to bring exhaust gas temperatures up so you can heat the catalyst very quickly and minimize heat losses in the exhaust track, which again comes back to SULEV.”
Beyond these two hardware highlights, Audi has made many smaller efficiency-enhancing improvements, including a governed steering pump, an optimized alternator, a variable-pressure oil pump and a significant increase in the temperature at which the coolant thermostat opens, from 189° F to 203° F (87° C to 95° C).
“And the engine retains its more-efficient intercooler, lower-friction internals, twin balance shafts, revised electronic controls, 6-hole fuel injectors, variable-nozzle turbocharger, variable valve timing and variable-length intake manifold,” writes Ward's AutoWorld Executive Editor Tom Murphy upon its announcement as a Ward's 10 Best Engines honoree.
Balkcom calls this engine “the workhorse of our brand and a cornerstone of our engine downsizing and future emissions compliance strategy to push efficiency even further without giving up performance.
“It's one of the best-balanced examples of efficiency and performance in the same package, without trade-offs, especially in North America,” he says.
He also points out that neither the I-6 in BMW's 328i nor the V-6s in the Lexus IS 250 and Mercedes-Benz C 300 come close to this turbocharged I-4's 258 lb.-ft. (350 Nm) of torque, or has a torque peak as low as its 1,500 rpm.
One disadvantage of a 4-cyl. vs. 6-cyl. can be troublesome noise, vibration and harshness characteristics, “but we've worked very hard to make sure that this engine lives up to Audi standards of refinement and NVH,” Balkcom says.
“We could have gone with an aluminum block, for example, but the cast-iron block has better damping properties.”
He adds that on a bench, independent of its vehicle application, the new EA-888 I-4 is 14% more fuel efficient than the older EA-113. In the '10 manual-transmission AWD A4 tested by Ward's editors, it delivers 22/30 mpg (10.7-7.8 L/100 km) city/highway.
Audi is well aware that buyers less concerned with fuel economy might be more attracted to its competitor's larger 6-cyl. offering, but the auto maker is undaunted.
“With a regulatory structure that puts all the burden on the manufacturer and none on the consumer, we've been the candle in the dark pushing four cylinders in the entry-luxury sedan segment,” Balkcom says.
“Competitors, so far, are meeting U.S. regulatory requirements with 6-cyl. engines, but we think they'll be forced to follow down the 4-cyl. path in those segments in the very near future.”
