The Ward’s 10 Best Engines competition has recognized outstanding powertrain development for 18 years. In this installment of the 2012 Behind the 10 Best Engines series, WardsAuto looks at development of GM’s power-dense Ecotec I-4 turbo.
The turbocharged 4-cyl. Ecotec engine in Buick's ’12 Regal GS pumps out 270 eager horses and 295 lb.-ft. (400 Nm) of tarmac-toasting torque from just 2.0L of displacement. That equals an astounding 135 hp/L, the highest specific output ever certified by the Society of Automotive Engineers.
That power easily beats similarly-sized I-4s from BMW, Audi, Volkswagen and others.
The Ecotec’s architecture was designed with future high-performance variants in mind, but General Motors powertrain engineers beefed it up further to accommodate higher output and temperatures while they also added gasoline direct injection, dual cam phasing (variable-valve timing) and twin-scroll turbocharging. This technology trio delivers near-instant response, largely by keeping exhaust pulses of cylinders one and four separate from those of cylinders two and three until they reach the lightweight turbine blades.
"This engine charges like an angry water buffalo when you get the revs up, and yet, it's silky smooth." raves WardsAuto editor Drew Winter.
The original, and larger, 2.2L Ecotec I-4 was developed by a 1994 partnership among GM’s U.S., European and Australian powertrain units. They put their best heads together to create an innovative, all-new engine to satisfy preferences and requirements around the world. The project was based at England’s Lotus Engineering, intentionally far away from the partners’ home organizations.
When their compact, lightweight and low-maintenance baby was born, it incorporated not just the best thinking and technologies from around the world but also provisions for additional technologies in the future, including turbocharging, piston oil cooling, dual (intake and exhaust) VVT and GDI.
All GM Ecotecs feature aluminum block and head, dual overhead cams with low-maintenance chain drives, four valves per cylinder, twin counter-rotating balance shafts, electronic throttle control, a full-circle transmission mount and direct-mount accessories (no belts) to reduce or eliminate noise and vibration sources. Also significant is a cast-in oil-filter housing that eliminates throwaway filters and the need to crawl under the car to change the oil.
The North American 2.4L Ecotec bowed in 2005 in front-wheel-drive small and midsize GM cars. In addition to increased displacement (bore and stroke) and a higher-performance cylinder block, it offered a long list of features, including a new cylinder head with larger combustion chambers and improved structure and cooling; dual VVT; surprisingly high 10.4:1 compression ratio; oil-jet piston and cylinder-wall cooling; a new 32-bit control processor; coil-on-plug ignition; and a block-mounted oil cooler.
A 260-hp, 260-lb.-ft. (350 Nm) 2.0L GDI turbocharged variant was offered in high-performance ’07 Pontiac Solstice and Saturn Sky sports cars, and soon after in Chevy Cobalt and HHR SS models. The high-performance Ecotec’s block was strengthened substantially, with enlarged bulkheads and bore walls. Its water jacket was deepened for added cooling and the cylinder head was specially molded aluminum. Pistons featured a more heat-resistant salt-core design with oil galleys and oil-jet cooling.
The little powerhouse earned praise for its muscle but also was criticized for lack of refinement. We suspect the latter was due to cost pressures and the fact it was designed for budget-priced cars.
At that point in the development, GM's Ecotec team could have rested on its laurels and focused on the all-new family of Ecotec I-4s scheduled to debut (starting with a naturally-aspirated 2.5L in the ’13 Chevy Malibu and a new 2.0L Turbo in the '13 Cadillac ATS) in mid 2012. But someone decreed there first would be a still-hotter variant of the existing I-4 turbo for a special Buick Regal.
"We said we need to go to the next level," says Mike Anderson, global chief engineer for GM's large (2.0L and greater) gasoline 4-cyl. engines. "We did not have tons of reserve at 260 hp and 350 Nm, but now we were going to 270 hp and 400 Nm, which was quite a challenge,” Anderson says.
“Every element was stretched to its limit, so we had to go through the engine with a fine-tooth comb: block, bulkheads, bearings, heads, head gaskets, everything you could imagine that would see higher pressure, more flow or more mechanical torque, and make sure it was up to the task."
GM leadership also requested this variant be developed 26 weeks faster than usual. The challenges involved in accomplishing those output levels while meeting all of GM's quality and durability requirements were toughened by doing it on an accelerated schedule, Andersen says.
Furthermore, the 2.0L had to be a credible replacement for a much larger V-6, so a top priority was being fun-to-drive.
"You just breathe on the throttle and it responds so quickly," Anderson says. "The character of that response – we call it elasticity – is unique, not like a naturally aspirated engine. When that turbo is spooling, it's so right now, and the torque curve is flat over a very wide range. And we have to control it down to that torque. If you left it uncontrolled, the thing could make 500 Nm, (369 lb.-ft.) well beyond what the engine and driveline can mechanically take."
The added power mostly comes from making the induction and exhaust systems freer flowing, while the torque boost is accomplished mostly through controller software, which GM has developed internally since last year.
"This has pushed our software to the limit," Anderson says. "Being able to do the densities required and get more accurate internal calculations of torque in all different conditions, at sea level, at altitude, extreme hot and cold. It's a very tough task to be able to estimate air accurately to know what's coming into the engine."
One interesting air-management technique is "scavenging," which involves running a lot of valve overlap to "over-stuff" the engine with intake air, then injecting the fuel after the valves close, something you can't do with conventional port fuel injection.
"With the boosted engine, the pressure of the intake air is higher than atmosphere and what's in the cylinder, so it shoves everything out,” Anderson says. “With a lot of overlap between intake and exhaust, it fills the cylinder and starts blowing across the engine and filling the exhaust, so there's nothing in there except pure air. Then you slam the valve shut and inject the fuel, which helps with response and low-end torque. You have time to do that at low engine speeds, but it's tougher at higher speeds."
A key challenge in designing any boosted engine typically is deciding on the size of the turbo. You can use a larger one to make a big power number or a smaller one for quick response. New twin-scroll designs make this choice easier, Anderson says.
“Twin-scroll lets you size the turbo to make big numbers but also gives you good response down low, especially when combined with the scavenging. It's the best of both worlds," he says.
It's interesting that even as we celebrate this Ward's 10 Best Engines winner, its replacement has been introduced and soon will hit the road in the ’13 Cadillac ATS. It's the same 2.0L displacement and generates the same 270 hp, but everything is new.
GM's new Ecotec family shares no common parts with its predecessor, save some fasteners. For starters, the new Ecotec engines wear their intake and exhaust systems on opposite sides than the old ones. This allows easier packaging in a wide variety of global vehicle architectures.
Anderson confirms that GM's new Ecotec 4-cyl. family will be even more efficient and refined than its outgoing counterparts, but we'll save that discussion for if and when one is named a future Ward's 10 Best Engines honoree. Although the competition continues to toughen each year, we wouldn't bet against that happening.