|
It
may have only two valves per cylinder and not an overhead cam in sight, but the
supercharged 6.2-litre V8 for the 2009 ZR1 Corvette 2009 packs a helluva wallop
– no less than 620hp! You won’t find any mention of fuel usage – or much else
that reflects wider environmental concerns – but here’s what the insides look
like.
|
When it arrives next northern summer, the 2009
Chevrolet Corvette ZR1 will be the most powerful and fastest production car ever
produced by General Motors, with performance provided by a new, supercharged
6.2L LS9 small-block V-8 engine.
Incorporating the engineering experience already
found in the Corvette Z06’s LS7 engine and the new-for-2008 6.2L LS3 of the
Corvette, GM Powertrain is targeting 100 horsepower per litre for the LS9, or
620 horsepower (462 kW), and approximately 595 lb.-ft. of torque (807 Nm).
The enabler of the LS9’s performance is a new,
large positive-displacement Roots-type supercharger – with a unique four-lobe
design – developed for the engine by Eaton. It is teamed with an integrated
charge cooling system that reduces inlet air temperature for maximum
performance. The LS9 represents the first of several new, supercharged
small-block engines that will be introduced in GM vehicles in the near future,
each using superchargers of similar design.
Performance
More than just its tremendous peak horsepower and
torque numbers, the supercharged LS9 makes big power at lower rpm and carries it
in a wide arc to 6,600 rpm. GM Powertrain testing shows the engine makes
approximately 300 horsepower (224 kW) at 3,000 rpm and nearly 320 lb.-ft. of
torque (434 Nm) at only 1,000 rpm. Torque tops 585 lb.-ft. (793 Nm) at about the
4,000-rpm mark, while horsepower peaks at 6,500 rpm.
The engine produces 90 percent of peak torque from
2,600 rpm to 6,000 rpm.
Heavy-duty and lightweight reciprocating
components enable the engine’s confident high-rpm performance, while the
large-displacement Eaton supercharger pushes enough air to help the engine
maintain power through the upper levels of the rpm band.
The LS9 is assembled by hand at GM’s Performance
Build Center, a unique, small-volume engine production facility in Wixom, Mich.,
that also builds the Corvette Z06’s LS7 engine and other high-performance GM
production engines.
Cylinder block and reciprocating parts
The LS9’s aluminium cylinder block features steel,
six-bolt main bearing caps, with enlarged vent windows in the second and third
bulkheads for enhanced bay to bay breathing.
Cast iron cylinder liners – measuring 4.06 inches
(103.25 mm) in bore diameter – are inserted in the aluminium block and they are
finish-bored and honed with a deck plate installed. The deck plate simulates the
pressure and minute dimensional variances applied to the block when the cylinder
heads are installed, ensuring a higher degree of accuracy that promotes maximum
cylinder head sealing, piston ring fit and overall engine performance.
Nestled inside the cylinder block is a forged
steel crankshaft that delivers the LS9’s 3.62-inch (92 mm) stroke. It features a
smaller-diameter ignition-triggering reluctor wheel and a nine-bolt flange – the
outer face of the crankshaft on which the flywheel is mounted – that provides
more clamping strength. Other non-supercharged 6.2L engines, such as the base
Corvette’s LS3, have a six-bolt flange.
A torsional damper mounted to the front of the
crankshaft features a keyway and friction washer, which also is designed to
support the engine’s high loads.
Attached to the crankshaft is a set of titanium
connecting rods and forged aluminium pistons, which, when combined with the
cylinder heads, delivers a 9.1:1 compression ratio. This combination is
extremely durable and lightweight, enabling the LS9’s high-rpm capability.
Cylinder head
The basic cylinder head design of the LS9 is
similar to the L92-type head found on the LS3 V8, but it is cast with a premium
A356T6 alloy that is better at handling the heat generated by the supercharged
engine – particularly in the bridge area of the cylinder head, between the
intake and exhaust valves.
In addition to the special aluminium alloy, each
head is created with a rotocast method. Also known as spin casting, the process
involves pouring the molten alloy into a rotating mould. This makes for more
even distribution of the material and virtually eliminates porosity – air
bubbles or pockets trapped in the casting – for a stronger finished product.
Although the heads are based on the L92 design,
they feature swirl-inducing wings that are cast into the intake ports. This
improves the mixture motion of the pressurized air/fuel charge. The charge
enters the combustion chambers via titanium intake valves that measure 2.16
inches (55 mm) in diameter. Spent gases exit the chambers through 1.59-inch
(40.4 mm) hollow stem sodium-filled exhaust valves. The titanium intake and
sodium-filled exhaust valves are used for their lightweight and high-rpm
capability.
To ensure sealing of the pressurized engine,
unique, four-layer steel head gaskets are used with the LS9’s heads.
Camshaft and valvetrain
The broad power band enabled by the LS9’s
large-displacement supercharger allows it to make strong low-end torque and
great high-rpm horsepower, which allowed engineers to specify a camshaft with a
relatively low lift of 0.555-inch (14.1 mm) for both the intake and exhaust
valves. This low-overlap cam has lower lift and slower valve-closing speeds than
the Z06’s 505-horsepower (377 kW) LS7, helping the LS9 – with its approximately
620 horsepower – deliver exemplary idle and low-speed driving qualities.
The camshaft actuates a valvetrain that includes
many components, including the lifters, rocker arms and valve springs, of the
LS3 engine. However, LS7 retainers are used to support the engine’s high-rpm
performance.
Supercharger and charge cooler
The LS9’s R2300 supercharger is a sixth-generation
design from Eaton, with a case that is specific to the Corvette application. The
supercharger features a new four-lobe rotor design that promotes quieter and
more efficient performance, while its large, 2.3-liter displacement ensures
adequate air volume at high rpm to support the engine’s high-horsepower
aspiration. Maximum boost pressure is 10.5 psi (0.72 bar).
The supercharger is an engine-driven air pump that
contains a pair of long rotors that are twisted somewhat like pretzel sticks. As
they spin around each other, incoming air is squeezed between the rotors and
pushed under pressure into the engine – forcing more air into the engine than it
could draw under “natural” aspiration. The rotors are driven by a pulley and
belt that are connected to the engine’s accessory drive system.
Because the pressurized air is hotter than
naturally aspirated air, the LS9 employs a liquid-to-air charge cooling system
to reduce inlet air temperature after it exits the supercharger – reducing the
inlet air temperature by up to 78 degrees C (140 F). Cooler air is denser and
allows the engine to make the most of its high-pressure air charge. The charge
cooling system includes a dedicated coolant circuit with a remote-mounted pump
and reservoir.
The design of the supercharger case and its
integrated charge cooling system was driven by the space and dimensions afforded
under the Corvette’s hood. To that end, the charge cooler was designed as a
“dual brick” system, with a pair of low-profile heat exchangers mounted
longitudinally on either side of the supercharger. Coupled with the supercharger
itself, this integrated design mounts to the engine in place of a conventional
intake manifold and is only slightly taller than a non-supercharged 6.2L engine.
The air inlet and rotor drive pulley are positioned at the front of the
supercharger.
Additional engine details
Oiling system
The LS9 uses a dry-sump oiling system that is
similar in design to the LS7’s system, but features a higher-capacity pump to
ensure adequate oil pressure at the higher cornering loads the ZR1 is capable of
achieving.
An oil-pan mounted oil cooler is integrated, too,
along with piston-cooling oil squirters located in the cylinder block. The
expanded performance envelope of the Corvette ZR1 required changes to the dry
sump system also used in the Z06. System capacity is increased and scavenge
performance improved to meet the demands of Chevrolet's highest-performance
sportscar.
Water pump
To compensate for the heavier load generated by
the supercharger drive system, an LS9-specific water pump with increased bearing
capacity is used.
Accessory drive system
To package the accessory drive system in the
Corvette’s engine compartment, the supercharger drive was integrated into the
main drive system. This required a wider 11-rib accessory drive system to be
used with the LS9 in order to support the load delivered by the supercharger.
Fuel system
The LS9 uses high-capacity 48-lb./hr. fuel
injectors with centre-feed fuel lines. The centre feed system ensures even fuel
flow between the cylinders with less noise. In order to ensure fuel system
performance during low speed operation as well as under the extreme performance
requirements of wide open throttle (WOT), a dual pressure fuel system was
developed. This system operates at 250 kPa at idle and low speed, and ratchets
up to 600 kPa at higher-speed and WOT conditions.
Throttle body
An 87-mm, single-bore throttle body is used to
draw air into the engine. It is electronically controlled.
Rocker covers / ignition
coils
Unique rocker covers with new, direct-mount
ignition coils are used. Other Gen IV engines, such as the LS3, feature coil
packs mounted to a bracket. The LS9’s direct-mounted coils offer a cleaner
appearance and a shorter lead between the coil and spark plug.
Specifications
|
Engine |
6.2L SUPERCHARGED V-8 (LS9) |
|
Displacement (cu in / cc): |
376 / 6162 |
|
Bore & stroke (in / mm): |
4.06 x 3.62 / 103.25 x 92 |
|
Block material: |
cast aluminium |
|
Cylinder head material: |
cast aluminium |
|
Valvetrain: |
overhead valve, 2 valves per cylinder |
|
Fuel delivery: |
SFI (sequential fuel injection) |
|
Compression ratio: |
9.1:1 |
|
Horsepower / kW: |
620 / 462 (est.) |
|
Torque (lb-ft / Nm): |
595 / 823 (est.) |
|
Recommended fuel: |
premium required |
|
EPA estimated fuel economy: |
TBD |
|