GM 2.5 Liter I4 Ecotec LCV Engine

The 2.5-liter inline four-cylinder LCV engine is produced by General Motors for use in several General Motors vehicles. The engine is part of GM’s new Ecotec engine family and replaces the 2.4-liter LEA and LUK.

Overview

GM’s versatile and technologically advanced Ecotec engine family expands with a new, larger 2.5L (LCV) variant. It is based on a new generation of large-displacement four-cylinder engines, which was designed for greater efficiency. GM proprietary computational fluid dynamics (CFD) analysis techniques were used to develop an all-new combustion system with a higher compression ratio.

The new combustion system features improved knock resistance and higher flowing intake and exhaust ports in the cylinder head which help increase efficiency, power, and torque. The new Ecotec also has increased authority cam phasing to minimize any compromise between efficiency, performance, emissions, and drivability. Like the current generation of technically advanced Ecotec engines, the 2.5L also features a high pressure direct injection fuel system, dual overhead camshafts with continuously variable valve timing, electronic throttle control, and pistons with jet-spray oil cooling.

Engine highlights:

• Engine Block: the Ecotec 2.5L’s sand-cast cylinder block is a superior refinement of previous Ecotec engine block castings. It is dimensionally similar with previous variants, while providing excellent structural support, as well as enabling greater control of noise, vibration and harshness.
  The main bearing bulkheads, which support the crank bearing, as well as the cylinder bore walls, have been significantly strengthened to support increased engine loads. Also, refinements to the oil distribution system enable improved oil flow throughout the engine; and an expansion of the coolant jacket, along with the use of cast-in-place bore liners, allows more precise bore roundness and improves the block’s ability to dissipate heat.
• Aluminum Pistons with Jet-Spray Cooling: the Ecotec 2.5L’s pistons use lightweight aluminum pistons, for less reciprocating mass inside the engine that enhances efficiency, decreases vibration and bolsters the feeling of performance as rpm increases.
  Each piston has its own directed jet that sprays oil toward its skirt, coating its underside and the cylinder wall with an additional layer of lubricant. The extra lubrication cools the pistons, reducing friction and operational noise, while also bolstering the engine’s durability.
  The pistons are used with durable yet lightweight forged powdered metal connecting rods.
• Cylinder Head: the 2.5L LCV has a 356T6 aluminum cylinder head that is cast with advanced semi-permanent mold technology. This provides excellent strength, reduced machining and optimal port flow. There is no need for heat treatment to the casting, which reduces residual stress and, consequently, enhances the engine’s durability.
  The cylinder head is designed specifically for direct injection into each combustion chamber. This is accomplished by positioning an injector under the intake port of each cylinder, so it protrudes into the chamber. The combustion chambers and ports are optimized for direct injection and high port flow.
  The cylinder head includes premium valve seat, valve guide and valve materials. They were selected for minimum wear while operating in more severe conditions associated with direct injection. These premium materials, along with a hydraulic lash-adjusting lifter, ensure good durability without required lash adjustments.
  The cylinder head also has integral cast oil passages that feed a set of internal oil control valves that activate cam phasers, enabling variable valve timing.
• DOHC with Continuously Variable Valve Timing: overhead cams are the most direct, efficient means of operating the valves, while four valves per cylinder increase airflow in and out of the engine. This arrangement is integrated on the Ecotec 2.5L’s lightweight aluminum cylinder head.
  Both the intake and exhaust cams have hydraulically operated vane-type phasers that are managed by a solenoid and directed by the engine control module (ECM). The phasers turn the camshaft relative to the drive sprocket, allowing intake and exhaust valve timing to be adjusted independently.
  Cam phasing changes the timing of valve operation as conditions such as rpm and engine load vary. It allows an outstanding balance of smooth torque delivery over a broad rpm range, high specific output and good specific fuel consumption. Cam phasing also provides another effective tool for controlling exhaust emissions. Because it manages valve overlap at optimum levels, it eliminates the need for a separate exhaust gas recirculation (EGR) system.
• Direct Injection: direct injection moves the point where fuel feeds into an engine closer to the point where it ignites, enabling greater combustion efficiency. It fosters a more complete burn of the fuel in the air-fuel mixture and it operates at lower temperature than conventional port injection. This allows the mixture to be leaner (less fuel and more air), so less fuel is required to produce the equivalent horsepower of a conventional, port-injection fuel system. Direct injection also reduces emissions, particularly cold-start emissions, by about 25 percent.
  With direct injection, the higher compression ratio is possible because of a cooling effect as the injected fuel vaporizes in the combustion chamber. This reduces the charge temperature and lessens the likelihood of spark knock. The direct injection fuel injectors have been developed to withstand the greater heat and pressure inside the combustion chamber and also feature multiple outlets for best injection control. The fuel system operates at pressure as high as 2,250 psi, compared to about 60 psi in conventional port injected engines.
• Cam-Driven High-Pressure Fuel Pump: a high-pressure, cam-driven pump provides the fuel pressure required of the direct injection system in the Ecotec 2.5L. The engine-mounted fuel pump is augmented by a conventional electrically operated supply pump in the fuel tank. The fuel delivery system features a high-pressure stainless steel feed line and a pressure-regulated fuel rail, without a conventional fuel return line from the engine to the tank. Fuel pressure varies from about 750 psi at idle to 2,250 psi at wide-open throttle.
• Two-Stage Thermostat: the coolant thermostat’s operating point is electronically controlled to optimize engine temperatures during different phases of operation to enhance fuel efficiency. The engine control module monitors sensors and controls the thermostat based on mapping that takes into account the wide range of engine operating conditions, including temperature and load. The thermostat opens partially at 194 degrees F (90 C) and fully at 221 degrees F (105 C).
• Two-Stage, Variable-Displacement Oil Pump: the variable-flow oiling system helps maximize fuel efficiency. Rather than the linear operation of a conventional fixed-flow pump, it is accomplished with a crankshaft-driven oil pump that matches the oil supply to the engine load. The engine’s variable-flow pump changes its capacity based on the engine’s demand for oil. This prevents using energy to pump oil that is not required for proper engine operation.
  The flow volume of the oil pump is designed to support the Ecotec 2.5L’s oiling requirements that include piston cooling and camshaft phasing. The cam phasers are supplied with oil through separate bores in the cylinder block and head. The recirculation of the increased amount of oil in the cylinder head is permitted through additional pre-cast oil return channels.
• Relocated Balance Shafts: the 2.5L LCV’s balance shafts – which are commonly used in four-cylinder engines to reduce vibration – are located in a cassette in the oil pan. It’s a move from previous Ecotec engines’ cylinder block-mounted shafts, which helps reduce noise through three key design features: a shorter, quieter drive chain, precision shaft-to-shaft reversing gears and light drag torque from driving the oil pump.
  The short drive chain eliminates the previous long, winding “bushed” chain that included driving the water pump. It uses a premium inverted tooth chain design instead of a conventional roller-type chain, for quieter performance. The shaft-to-shaft reversing gear set allows the drive gears of the shafts to mesh directly, eliminating the need for a chain to “back drive” the second shaft, which must rotate in the opposite direction of the first shaft. The second shaft also drives the oil pump, providing a light drag torque to pre-load the reversing gear teeth for smooth, rattle-free and quiet operation.
• In-Pan Oil Pump Assembly: another significant change from previous Ecotec engines is the relocation of the oil pump assembly from the front of the crankshaft to within the oil pan, where it is driven by the second balance shaft. This reduces noise from the front cover area – an aluminum-intensive area that radiates noise – and provides a small drag torque to ensure quiet balance shaft gear operation. Also, the oil-sump location minimizes the potential for pump cavitation noise.
• Camshaft Drive with Inverted-Tooth Chain: like the drive chain for the balance shafts, the camshaft drive chain uses a premium, inverted-tooth design that is significantly quieter than a roller-type chain. As its name implies, an inverted-tooth chain has teeth on its links – two-pin rolling pivot joints – that essentially wrap around the gear sprocket to take up virtually all the tension. This allows for smoother meshing of the chain links to the sprocket teeth, the cause of most noise in chain drive systems. The chain-to-sprocket tooth impact is greatly reduced with the inverted-tooth design (also known as a silent chain drive), which virtually eliminates noise and enhances durability.
• Two-Piece Oil Pan: when it came to the oil pan, engineers faced a conundrum: Aluminum provides stiffening structure to an engine, but it radiates noise. Stamped steel, on the other hand, radiates less noise, but doesn’t offer the structural benefits needed for a stiff powertrain assembly. Their solution was to combine the materials to create a unique, two-piece oil pan that features a stiff aluminum upper section to support the engine’s structure – maintaining the Ecotec engine’s signature full-perimeter transmission mounting surface – and a stamped steel lower section to provide greater overall sound performance.
• Structural Camshaft Cover: as a cast-aluminum part mounted on the very top of the engine assembly, the camshaft cover can be a significant source of noise. That’s not the case with the 2.5L, thanks to a new, structural cover design that is stiffer and mounts more rigidly to the engine. It features increased ribbing and additional attachment bolts down the center, all of which increase the cover’s stiffness to help push the engine’s sound frequency above 2,000 hertz. It also enables excellent oil sealing for valvetrain oil control passages integrated within the cover.
• Acoustic Intake Manifold Cover: like many engines in the segment, the 2.5L uses a composite plastic lightweight intake manifold. But plastic conducts noise, so engineers wrapped the intake with a clamshell-like isolating cover. It has a sound-absorbing “blanket” on the inside that snugs against the intake to provide isolation, plus the cover has a visually clean outer layer, which works as a noise barrier.
• Forged Steel Crankshaft: engineers selected a forged steel crankshaft for the 2.5L because, along with its strength and durability, it is stiffer than a conventional cast iron crankshaft. That reduces noise and vibration at mid- and high-rpm levels, enhancing the engine’s smoothness.
• Iron Main Bearing Cap Inserts: iron inserts are cast into the 2.5L’s aluminum cylinder block bedplate, enhancing the structure at the main bearings, for greater smoothness and quietness. The bedplate provides stiffness to the bottom of the cylinder block and incorporates the main bearing caps – components used to secure the crankshaft within the block. The iron insert material ensures close main bearing tolerances over a wide range of engine operating temperatures, for quieter engine lower-end noise.
• Isolated Fuel Rail: although not new to the 2.5L, its isolated fuel rail nonetheless helps achieve overall quietness. Like the Ecotec 2.4L and Ecotec 2.0L turbo, the 2.5L features direct injection, which employs a very-high pressure fuel system, including an engine-mounted fuel pump and complementing fuel injectors that “fire” with very high pressures directly into the combustion chambers. This can be a source of noise. The fuel rail is a tube-like component that supplies gasoline to the injectors. To reduce the noise associated with this efficiency-enhancing system, the injectors are suspended and the fuel rail is attached to the cylinder head with rubber-isolated, compression-limiting mounting provisions.
• Structural Front Cover: similar to the structural camshaft cover described above, the 2.5L’s front cover, which covers both the camshaft drive system and balancer drive systems, was designed with extra ribbing and secured with extra fasteners – including a new row of attachments down the middle of the cover. Like the camshaft cover, the result is a stiffer, more rigid, quieter cover that contributes to lower engine noise.

Specifications

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