IMPROVING AN ALREADY STURDY DESIGN
A lot of development work went into this new version of the Ecotec; it
wasn't simply a matter of plunking a turbo on the engine. Indeed, every
major casting was redesigned to provide a heightened level of
reliability, though the engine was originally designed for use in
forced-induction applications.
As with the new supercharged Northstar engine in the new Cadillac XLR,
the displacement of the Solstice GXP's is slightly smaller than the
normally aspirated version. Both feature a reduced bore size to
increase cylinder-wall thickness. The Ecotec Turbo's stroke is also
reduced and features a beefy, forged-steel crankshaft for additional
durability. Bore and stroke are 86x86 mm (3.38x3.38 inches) for a total
displacement of 1,998 cc's or 122 ci.
The Ecotec 2.0-liter Turbo uses a stronger "Gen II" Ecotec engine
block, which was developed with input from racing experience to support
increased horsepower and torque. Cylinder-block bulkheads -- the areas
where the main bearing caps are attached -- and the cylinder walls are
enlarged for strength. Other areas of the engine were enhanced to
reinforce the structure, and the water jacket is deeper for added
cooling capacity and improved cylinder-bore roundness. This
architecture is shared with the 2.4-liter Ecotec engine that debuted in
the Pontiac Solstice roadster.
Its bottom end is also upgraded to handle the additional boost. In
addition to the forged-steel crankshaft, the Ecotec Turbo also employs
forged connecting rods and cast pistons. The pistons feature a dish
shape that deflects injected fuel toward the spark plugs. They are
cooled with a jet-spray of oil on their undersides that directs the oil
into a cast-in channel inside the piston, further resisting detonation.
Additionally, the Ecotec 2.0-liter Turbo four benefits from variable
valve timing and an intercooled, twin-scroll turbocharger system to
provide boost. A dual-scroll design is used on the exhaust turbine and
speeds up velocity and response, much in the same way a two-plane
intake manifold performs the identical function. The result is a nearly
lag-free system, one that gives the 2.0-liter four the feel of a much
larger engine. Dual cam phasing complements the turbocharging by
optimizing valve timing at lower rpm for best turbo response and quick
engine build-up time. "There is virtually no lag with this system,"
says Ed Groff, assistant chief engineer, Ecotec 2.0-liter Turbo engine.
"Throttle response is immediate. The engine acts like it has a larger
displacement engine."
Its turbocharger provides up to approximately 20 pounds of boost. It is
matched to the engine's displacement and performance objectives, and is
supported by the air-to-air intercooling system, which reduces inlet
temperature pf the turbo-compressed air by approximately 212 degrees
(100 degrees C), enhancing performance because cooler air is denser.
DIRECT INJECTION
Perhaps the most innovative feature of the new turbocharged Solstice
powerplant is the direct injection system. Essentially, the system
locates the injector in the combustion chamber rather than in the
intake manifold runner or intake port. This arrangement is similar in
layout to a diesel powerplant, exposing the injector to the heat and
pressure of the combustion event. Unlike a diesel, the Eccotec uses a
conventional spark plug and otherwise operates as a normal four-cycle
spark-ignition engine. The system is referred to as Spark Ignition
Direct Injection (SIDI).
With fuel delivered directly to the combustion chamber to create a more
complete burn of the air/fuel mixture, less fuel is required to produce
the equivalent horsepower compared to a conventional port-injection
system, particularly at normal cruising speeds. "Direct-injection
technology works well with turbocharging and helps deliver a great
balance of power and economy," says Groff. "The Ecotec 2.0-liter Turbo
produces the power expected of a V-6, but in a smaller, more efficient
pacckage -- and the driving response is simply terrific."
To accomodate the direct-injection system, the Ecotec 2.0-liter Turbo
has a unique cylinder head and intake manifold. The cylinder head
incorporates mounting locations for the fuel injectors -- which are
typically mounted in the intake ports or intake manifold on port
injection engines. A high-pressure fuel pump delivers fuel to a
variable-pressure fuel rail. Fuel enters the combustion chamber through
multihole fuel injectors. The fuel pump, fuel-rail pressure, fuel
injection timing, and injection duration are controlled by the engine
control module. In this way, fuel is metered and delivered in a finely
atomized spray, which, during the intake stroke, is introduced into the
chamber near the intake valves, in direct line of the spark plug. SIDI
also permits a slightly higher compression ratio than if the fuel were
delivered with conventional fuel injection and allows the mixture to be
leaner at full power.
A high-pressure, returnless fuel system is employed for this
application. It features a high-strength stainless steel fuel line that
feeds a variable-pressure fuel rail. Direct injection requires higher
fuel pressure than conventional fuel injected engines, and an
engine-driven high-pressure fuel pump is used to supply up to 2,250 psi
of pressure. This system regulates lower fuel pressure at idle --
approximately 752 psi and higher pressure at wide-open throttle. The
cam-driven, high-pressure pump works in conjunction with a conventional
fuel tank-mounted supply pump.
Apart from the mounting position of the fuel injectors, the cylinder
head has conventional port and combustion designs, although both are
optimized for direct injection and high boost pressures. Sodium-filled
exhaust valves and stainless steel exhaust manifold are durable
components designed to stand up to the high-performance capability of
the engine.
A unique cylinder head, fuel system, pistons, intake manifold, and the
dual-scroll turbocharger are the olny major ccomponents that
differentiate the 2.0-liter Turbo from other members of the Ecotec
engine family. Mobil 1 synthetic engine oil is added at the factory.
Synthetic oil was selected for its friction-reducing capabilities and
high-temperature performance.
DUAL CAM PHASING
The camshafts of the Ecotec 2.0-liter Turbo engine have phasers that
support the continuously variable intake and exhaust valve timing. They
also have cam position sensors, so that the engine control module can
accurately control valve timing. The crankshaft and camshaft position
sensors are digital. A new engine controller, specific to this
powerplant, is used to sense and dictate its performance parameters.
Variable intake and exhaust timing works synergistically with both the
gasoline direct injection and turbocharging systems. The variable
engine timing enabled by cam phasing allows the combustion process to
be optimized. Also, valve "overlap" at low rpm can be adjusted by the
controller to increase the response of the turbocharger, providing a
more immediate feeling of power.
ECOTEC ENGINE FAMILY
The Ecotec 2.0-liter Turbo is built on a global platform that was
designed at the outset for a range of performance and combustion
capabilities. Gen II blocks support the high-performance demands of the
engines, but are merely a strengthened version of the original Ecotec
architecture. The oil pump, for example, is the same as used in all
other Ecotec engines. It was originally designed to support
high-performance applications of future engines.
"This 2.0-liter Turbo is the pinnacle of Ecotec performance to date,
with additional growth planned," says Groff. The groundwork for its
capabilities was laid on the drawing table at the beginning of the
Ecotec's development. Prior work and a far-thinking engine design
continue to help GM respond to market demands around the globe more
quickly and with greater accuracy."
This new Ecotec family member also features:
- Dual overhead camshafts (DOHC) and four valves per cylinder
- Twin counter-rotating balance shafts for operational smoothness
- "Drive by Wire" electronic throttle control
- Low friction, roller-finger follower valvetrain with hydraulic lash adjusters
- Low-maintenance chain-drive for the camshafts
- Direct-mount accessories, which reduce or eliminate traditional sources of noise and vibration
- Full-circle transmission to reduce noise and vibration
- GM Oil Life System, which can reduce the frequency for oil changes
- Innovative cast-in oil filter housing, which eliminates
the need to crawl under the vehicle to perform oil changes and
eliminates throwaway oil filter cans that retain used oil.
- As with other engines in the Ecotec family, the 2.0-liter
Turbo engine also has premium features designed to ensure smooth and
quiet operation, including a polymer coating and skirt design for the
pistons that reduce noise during cold starts. An automatic hydraulic
tensioner also is used to maintain optimal tension on the timing chain,
which reduces noise and vibration.
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