GM Powertrain's new Ecotec 2.4-liter four-cylinder engine, slightly modifies that well-used adage, "There’s no substitute for cubic inches." In the case of this slightly larger version of the original Ecotec 2.2-liter, one of GM's highest-volume engine families, there are a few more cubic inches found in the new 2.4-liter variant. But along with the larger displacement, which has become vital in the increasingly competitive compact-car segment, the 2.4-liter for the first time brings variable valve timing to the Ecotec modular engine family.

"We have added technology to improve low-end torque and continue to reduce emissions," said Jay Subhedar, Ecotec global four-cylinder engine assistant chief engineer. "For the new Ecotec, variable valve timing helps deliver 90 percent of the torque peak at as low as 2400 rpm. That sort of responsiveness enormously enhances engine response."

The combination of slightly more displacement and variable valve timing enables the Ecotec 2.4-liter to achieve one of the highest torque ratings – an estimated 170 lb.-ft. – for a 2.4-liter normally aspirated four-cylinder in the United States And the Ecotec 2.4-liter's 170 horsepower at 6000 rpm also is one of the highest specific-power outputs for any non-boosted four-cylinder of any size sold in the U.S., according to Ward's 2003 market data.

The new Ecotec 2.4-liter engine's torque-rich power delivery and its designed-in refinement deliver a driving experience that will please both performance-oriented buyers and those simply seeking a more sophisticated feel from a compact-car powertrain.

Intelligent Technology as Important as Cubic Inches

Increasing displacement is perhaps the most-proven technique to improve horsepower and torque, and that’s where GM Powertrain engineers started when developing the Ecotec 2.4-liter. For the new 2.4-liter variant, both cylinder bore and stroke are increased in relation to the original Ecotec 2.2-liter engine. The new engine's bore is 88 mm and stroke is 98 mm, versus the 2.2-liter's 86-mm bore and 94.6-mm stroke. These increases, multiplied by each of the Ecotec 2.4-liter’s four cylinders, yield a total displacement of 2,384 cubic centimeters versus the original 2.2-liter's 2,189 cubic centimeters.

But equally important to delivering class-leading torque is the Ecotec 2.4-liter’s new variable valve timing system, developed to enhance the low- and midrange torque output of the new engine.

The new variable valve timing system uses electronically controlled hydraulic camshaft phasers to alter the relationship of the intake and exhaust camshafts as much as 50 degrees relative to the crankshaft. Yet the system adds little weight or assembly complexity to the basic Ecotec DOHC architecture because the Ecotec family was designed from the beginning to easily accept technology advances such as variable camshaft phasing.

But the new Ecotec 2.4-liter's technology story hardly stops there. The new Ecotec enjoys a host of new technical enhancements:

• Electronic throttle control. The ETC system eliminates the physical connection between the accelerator pedal and the engine throttle. This well-proven "drive-by-wire" control allows for remarkably precise engine control and response, while simultaneously enhancing the engine’s interface with other vehicle systems.
• An all-new, engine control module (E67). The Ecotec 2.4-liter is one of the first GM engines to employ this sophisticated new controller that leverages 32-bit processing power. It incorporates 32 megabytes of burst flash memory and 32 kilobytes of external RAM and 36 kilobytes of internal RAM, as well as a high-speed CAN bus to deliver optimal networking capability.
• All engine-related sensors for the Ecotec 2.4-liter are digital rather than analog. “Digital sensors are more accurate and provide improved reliability,” said Subhedar of this emerging trend in engine-monitoring technology. The digital sensors improve information processing and reliability, which in turn means more-efficient engine performance.
• Individual coil-on-plug ignition modules improve upon the two-coil "cassette" of the original Ecotec design. The individual ignition modules for each spark plug enhance combustion and engine energy efficiency.
• Twin counter-rotating balance shafts, inherent in the Ecotec engine architecture, spin at twice the speed of the engine crankshaft to cancel the second-order vertical shaking forces experienced by inline four-cylinder engines. The balance shafts are driven by the quiet and efficient, zero-maintenance chain-drive system that operates the engine's camshafts and water pump

Ecotec's Robust Design, Structure Enhanced for New 2.4-Liter Variant

Along with significant new technology additions, the new Ecotec 2.4-liter enjoys numerous upgrades to the robust basic Ecotec engine architecture. The Ecotec design, already noted for impressively low levels of noise and vibration, includes features like a structural oil pan; full-circle transmission mounting flange; a highly rigid lower crankcase with four-bolts at each bulkhead; long cylinder-head bolts to assure robust clamping of the cylinder head to the engine block; and direct-mounted accessories to eliminate these traditionally large contributors to engine noise, vibration and harshness.

The Ecotec 2.4-liter's basic structure has been enhanced in several significant ways to ensure the engine's increased displacement and power do not compromise the Ecotec's high levels of inherent refinement. "In the global engine family, we look at various engine components to evaluate which are the right 'fit' for any given engine application," said Subhedar. "Commonality is a vital part of the Ecotec program – it's like an interlocking puzzle. We try to choose the best combination of components from the myriad of available technologies.”

Thus the Ecotec 2.4-liter leverages several heavy-duty components and systems borrowed from the high-performance Ecotec supercharged 2.0-liter engine program, plus many that are unique to the new 2.4-liter variant:

• An auxiliary oil cooler that is approximately 30 percent smaller than similar-capacity oil coolers used on other engines.
• Piston-cooling oil jets spray the underside of each piston with a continuous bath of engine oil, increasing longevity by reducing engine operating temperatures.
• Redesigned cylinder head with structural improvements and new multi-layer steel gasket.
• New camshafts with optimized lobe profiles.
• Enhanced lubrication system to provide for the extra requirements of the camshaft phasers and piston-cooling jets, along with a deeper oil sump to handle the higher potential cornering forces.

The Ecotec 2.4-liter will be built at GM Powertrain's Spring Hill, Tennessee, assembly facility. The 2.4L Ecotec will be launched in the all-new 2005 Chevrolet Cobalt, and is reportedly slated for use in 2005 or 2006 model year Saturns.

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Source: General Motors