2015 6.2L V-8 Supercharged (LT4)
Vehicle Applications
Chevrolet Corvette Z06
Overview
The LT4 6.2L supercharged V-8 engine is the power behind the Corvette Z06 and is the most
powerful production engine ever offered in a General Motors vehicle.
The new LT4 engine builds on the design strengths of the previous LS9 supercharged engine
used in the sixth-generation Corvette ZR1 and leverages the technologies introduced on the
seventh-generation Corvette Stingray, including direct injection, cylinder deactivation and
continuously variable valve timing, to take Corvette performance to an all-new plateau.
The new LT4 engine is based on the same Gen 5 small block foundation as the Corvette
Stingray’s LT1 6.2L naturally aspirated engine, incorporating several unique features designed
to support its higher output and the greater cylinder pressures created by forced induction,
including:

Rotocast A356T6 aluminum cylinder heads that are stronger and handle heat better than
conventional aluminum heads

Lightweight titanium intake valves

Forged powder metal steel connecting rods which are highly machined to an optimized
geometry for increased strength while eliminating unnecessary reciprocating mass

High 10.0:1 compression ratio – for a forced-induction engine – enhances performance
and efficiency and is enabled by direct injection

Forged aluminum pistons with unique, stronger structure to ensure strength under high
cylinder pressures

Stainless steel exhaust manifolds for structure at higher temperatures

Aluminum balancer for reduced mass

Standard dry-sump oiling system with a dual-pressure-control oil pump.
Cylinder block
The LT4’s Gen-V aluminum cylinder block shares two key design elements with GM’s original
small-block V-8: a 90-degree cylinder angle and 4.400-inch bore centers. The bore and stroke
dimensions are: 4.06-inch (103.25 mm) bore x 3.62-inch (92 mm) stroke.
Compared to the previous Gen-IV small block, the Gen-V’s aluminum cylinder block casting is
all-new, but based on the same basic architecture. It was refined and modified to accommodate
the mounting of the engine-driven fuel pump and vacuum pump. It also incorporates new engine
mount attachments, new knock sensor locations, improved sealing and oil-spray piston cooling.
Rotating assembly and windage tray
Within the Gen-V block is a durable rotating assembly that includes a steel crankshaft and
6.125-inch-long, powder-metal connecting rods, as well as high-strength, forged aluminum
pistons. The LT4’s connecting rods are based on the design of those used in the LT1, but are
specially machined for lower weight – an attribute that reduces reciprocating mass and enables
the engine to rev more quickly.
The crankshaft in the Gen-V small block is located with new nodular main bearing caps – a
significant upgrade over more conventional grey iron main caps. Nodular caps are stronger and
can better absorb vibrations and other harmonics to help produce smoother, quieter
performance.
A windage tray is also used with the Gen-V engine, which enhances performance and efficiency
by improving oil flow control and bay-to-bay crankcase breathing. The cylinder block and main
bearing caps maintain the optimal crankcase “windows” that were perfected on the Gen-IV
engine.
The LT4 has 10:1 compression ratio, which is comparatively high for a supercharged engine,
but it is enabled by the more precise fuel control of direct injection.
Forged Aluminum Pistons
The LT4 uses unique forged aluminum pistons with a structure designed for the more intense
cylinder pressures that come with forced induction. They also have a unique head topography
that is essential to the direct injection system. The “bowl” and shape of the top of the piston
head is designed to promote thorough mixing of the air and fuel – a dished center section helps
direct the fuel spray from the injector – to ensure complete combustion, which improves
performance and efficiency, particularly on cold starts.
To further reduce wear, the piston skirt is coated with a polymer material, which eliminates bore
scuffing, or abrasion of the cylinder wall over time from the piston's up-down motion. The
polymer coating also dampens noise generated by the piston's movement. The wrist pins, which
attach the piston to the connecting rod, were developed for maximum durability, with a large
outer diameter and a tapered inner diameter.
The pins "float" inside the rod bushing and pin bores in the piston barrel. Compared to a
conventional fixed pin assembly, in which the connecting rod is fixed to the piston's wrist pin and
the pin rotates in the pin bore, the floating pins reduce stress on the pin. They allow tighter pin
to pin-bore tolerances and reduce noise generated as the piston moves through the cylinder.
The benefit is less engine wear, improved durability and quieter operation.
Oiling System
The oiling system is revised and features a new, dual-pressure-control and variabledisplacement vane pump with increased flow capacity. As with the Gen-III/Gen-IV engines, the
oil pump is driven by the crankshaft. Variable displacement enables the pump to efficiently
deliver oil pump flow as demanded. Dual pressure-control enables operation at a very efficient
oil pressure at lower rpm coordinated with the Active Fuel Management and operation at a
higher pressure at higher engine speeds providing a more robust lube system with aggressive
engine operation.
The LT4 engine features a dry-sump oiling system with a 10.5-quart capacity. All Gen-V engines
are designed to be used with GM’s Dexos semi-synthetic motor oil. “Thinner” oil is used, too,
which helps reduce friction to enhance efficiency. The LT4 6.2L uses 5W30.
Oil-Spray Piston Cooling
All Gen-V engines feature oil-spray piston cooling, in which eight oil-spraying jets in the engine
block drench the underside of each piston and the surrounding cylinder wall with an extra layer
of cooling, friction-reducing oil. The oil spray reduces piston temperature, promoting extreme
output and long-term durability. The extra layer of oil on the cylinder walls and wristpin also
dampens noise emanating from the pistons.
PCV-Integrated Rocker Covers
One of the most distinctive features of the Gen V family is its domed rocker covers, which house
a patent-pending, integrated positive crankcase ventilation (PCV) system that enhances oil
economy and oil life, while reducing oil consumption and contributing to low emissions. The
rocker covers also hold the direct-mount ignition coils for the coil-near-plug ignition system.
Between the individual coil packs, the domed sections of the covers contain baffles that
separate oil and air from the crankcase gases – about three times the oil/air separation
capability of previous engines.
Camshaft Design
A refined camshaft helps balance the LT4’s remarkable output with silky, tractable low-rpm
operation. The camshaft operates the engine's valves and its design is crucial to both power
and smoothness. The torque-enhancing benefits of the supercharger allowed engineers to
develop a “softer,” lower-lift camshaft for the LT4, compared to the typical high-rev, high-power
exotic car engine. The result is smooth operation at low speed, particularly at idle.
The hydraulic roller-lifter camshaft’s specifications lift include: 0.492”/0.551” intake/exhaust lift,
189/223 crank angle degrees intake/exhaust duration at 0.050 tappet lift and a 120 degree cam
angle lobe separation.
Dual-Equal Cam Phasing
All Gen V engines feature dual-equal camshaft phasing (variable valve timing), which works with
Active Fuel Management to enhance fuel economy, while also maximizing engine performance
for given demands and conditions.
At idle, for example, the cam is at the full advanced position, allowing exceptionally smooth
idling. Under other conditions, the phaser adjusts to deliver optimal valve timing for
performance, driveability and fuel economy. At high rpm it may retard timing to maximize airflow
through the engine and increase horsepower. At low rpm it can advance timing to increase
torque. Under a light loads, it can retard timing at all engine speeds to improve fuel economy.
A vane-type phaser is installed on the front of the camshaft to change it’s angular orientation
relative to the sprocket, thereby adjusting the timing of valve operation on the fly. It is a dualequal cam phasing system that adjusts camshaft timing at the same rate for both intake and
exhaust valves. The system allows linear delivery of torque, with near-peak levels over a broad
rpm range, and high specific output (horsepower per liter of displacement) without sacrificing
overall engine response, or driveability. It also provides another effective tool for controlling
exhaust emissions.
The vane phaser is actuated by hydraulic pressure and flow from engine oil, and managed by a
solenoid that controls oil flow to the phaser.
Cylinder Head Design
The Gen-V small-block’s cylinder head design builds on the excellent, racing-proven airflow
attributes of previous small-block heads and matches it with a direct-injection combustion
system. It supports tremendous airflow at higher rpm for a broad horsepower band, along with
strong, low-rpm torque.
Compared to other Gen-V variants, the LT4 uses aluminum cylinder heads produced with a
rotocast manufacturing process, which rotates the head mold as the molten alloy cools and
essentially eliminates porosity, or microscopic pockets of air trapped in the casting. Rotocasting
delivers a stronger part that helps maintain performance and structural integrity over the life of
the engine.
The heads are cast in a premium A356T6 alloy, which better manages the heat generated in a
supercharged engine. A356T6 also pays dividends in the thinner bridge area between the intake
and exhaust valves, where effective heat dissipation is crucial to both performance and longterm durability.
Compared to the naturally aspirated LT1 head, which features 59.02cc combustion chambers,
the LT4 has a slightly larger 65.47cc chamber size designed to complement the volume of the
piston’s dish. The chamber size and piston dish work together to produce a 10:1 compression
ratio – a full 1.5 points lower than the LT1’s 11.5:1 compression. Lower compression than a
comparable naturally aspirated engine is required of a supercharged application to stave off
knock or detonation that can occur as a result of the forced-induction engine’s higher cylinder
pressures.
As with other Gen-V variants, the LT4 head features large, straight and rectangular intake ports
that feature a slight twist to enhance mixture motion. This is complemented by a reversal of the
intake and exhaust valve positions as compared to the Gen-IV design. The exhaust port shapes
are optimized for the new valve locations, with new port opening locations at the manifold face.
Large, lightweight valves are used in the LT4’s heads, including 2.13-inch (54mm) titanium
intake and 1.59-inch (40.4mm) hollow sodium exhaust valves. The exhaust valves are
manufactured from a high-chromium steel alloy called 21-43 (SilChrome 1 is used at the tip
only, the valve is made from 21-43). At normal operating temperatures, the sodium inside the
valve stem melts and becomes liquid. The liquid sodium improves conductivity, promoting heat
transfer away from the valve face to the cooler end of the stem, where it more readily dissipates
through the valve guide. This maintains a lower, more uniform valve temperature, reducing wear
on the valve seat for a consistent seal between the valve and head over the life of the engine.
The valves are held at 12.5 degrees intake/12 degrees exhaust angles vs. the Gen-IV’s 15degree angle. Additionally, the valves are splayed at 2.61 degrees intake/2.38 degrees exhaust
to reduce shrouding and enable greater airflow.
Valvetrain components include durable valve springs and roller-pivot rocker arms with a 1.8
ratio – the amount of movement on the valve side of the rocker arm in comparison with the
pushrod side. And speaking of pushrods, the Gen-V small-block features large-diameter 8.7mm
(outside diameter) components that provide exceptional stiffness that enables excellent highspeed valvetrain dynamic performance.
Given the LS4's pressurized induction, special attention was paid on sealing, too. The head
gaskets are extra-robust, seven-layer stainless steel, and the 12mm cylinder head bolts are
hardened stainless.
Next-generation Eaton supercharger
State-of-the-art supercharging technology is the foundation of the LT4’s remarkable
performance. The supercharger is an air pump driven by the engine’s crankshaft. It forces more
air into the engine's combustion chambers than the engine could otherwise draw on its own.
The increased volume of oxygen allows the engine to efficiently process more fuel, and thus
generate more power.
The LT4 employs Eaton’s new, twin-rotor R1740 Twin Vortices Series (TVS) supercharger,
which spins up to 20,000 rpm – 5,000 rpm more than the supercharger on the previous LS9
engine. The rotors are smaller in diameter than the LS9’s supercharger, which contributes to
their higher-rpm capability – and enables them to produce power-enhancing boost earlier in the
rpm band. That boost is achieved more efficiently via a more direct discharge port that creates
less turbulence, reducing heat and speeding airflow into the engine.
The LT4 supercharger displaces 1.7L and generates maximum boost pressure of 9.71 pounds
per square inch (0.67 bar). The TVS rotor design features four lobes on each of the
supercharger’s pair of rotors. The spiral-shaped rotors intermesh with each other and the fourlobe configuration provides about 20 percent more airflow than conventional three-lobe designs,
as well as an improvement in thermal efficiency of up to 15 percent. Moreover, parasitic power
loss – the amount of power the engine uses to operate the supercharger – is reduced 35
percent. That improves both supercharger response time and the engine’s overall efficiency.
Even with its integrated supercharger/intercooler assembly mounted in the valley between the
cylinder heads, the engine is only about 1 inch (25 mm) taller than the Corvette Stingray’s LT1
engine.
An electronically controlled throttle is mounted to the supercharger inlet. It is a single-bore
design with an 87mm bore diameter and features a “contactless” design that is more durable
and enables greater control.
The design of the supercharger system incorporates advanced features for noise reduction.
The rear cover of the supercharger gear case has changed from an Aluminum casting to a
constained-layer damping material designed to absorb radiated noise from the supercharger
drive gears. Additionally, the supercharger lid has a constrained-layer damping panel
assembled over the discharge port to damp the high frequency content of the air pulsations
exiting the supercharger discharge port. This reduces the traditional “whine” noise associated
with superchargers and gives a refined yet powerful and pleasing sound to the engine.
Dual-Brick Air-to-Liquid Intercooler
An advanced intercooling system increases the LT4’s performance and extends its
supercharger's benefits. The engine’s charge cooler is integrated in the supercharger case
adjacent to the rotors, with two air-to-liquid cooling “bricks” that substantially lower the
temperature of air used in the combustion process.
Intercoolers are familiar features on supercharged and turbocharged engines. Similar in concept
to an engine’s radiator, intercoolers cool the air pumped by the charging device into the
cylinders. Cooler air is denser air, which means more oxygen in a given volume, resulting in
optimal combustion and more power. Traditionally, intercoolers look like small radiators
mounted somewhere outside the engine, with air fed into the engine through a plumbing
network.
The LT4’s intercooling system raises the bar in both packaging and efficiency. It uses two lowprofile, aluminum clamshell heat exchangers mounted longitudinally adjacent to the rotors in the
supercharger case. Air pumped by the supercharger flows directly through these bricks to the
intake ports on the cylinder heads without the need to channel the air through plumbing to the
front of the vehicle and back. The bricks are cooled by their own coolant circuit, with a remote
pump and heat exchanger mounted in front of the Corvette’s radiator. The temperature of air
fed to the LT4’s cylinder heads is reduced by up to 140 degrees F (60 degrees C), substantially
increasing the amount of oxygen available for the combustion process.
Direct Injection
Direct injection is featured on all Gen-V engines. This technology 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 a lower
temperature than conventional port injection. That 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 delivers reduced emissions, particularly cold-start
emissions.
The pistons play an integral role in the direct injection system, as they feature dished heads
designed to direct the fuel spray for a more complete combustion. Design of this advanced
combustion system was optimized after thousands of hours of computational analysis,
representing one of the most comprehensively engineered combustion systems ever developed
by General Motors.
To support the requirements of an engine producing approximately 40 percent more power than
the naturally aspirated LT1, the supercharged LT4 uses higher-capacity, 141 lb./hr fuel injectors.
The LT1 injectors are rated at 123 lb./hr.
High-Pressure Fuel Pump
The LT4 direct injection system features a new higher fuel pressure pump, capable of pressures
up to 20Mpa (200bar). The LT1 high pressure pump is capable of 15Mpa (150bar). Direct
Injection requires the high-pressure, engine-driven fuel pump in addition to a conventional, fueltank-mounted pump. On all Gen-V engines, the pump is mounted in the “valley” between
cylinder heads – beneath the intake manifold. It is driven by the camshaft at the rear of the
engine.
A “soft stop” control strategy for the pump’s internal solenoid significantly reduces the
characteristic “ticking” sound of direct injection systems. Mounting the pump in valley, where it is
covered by an acoustically treated intake manifold, also helps reduce noise, while also
maintaining the tight, compact packaging for which all small-blocks have been known.
Active Fuel Management
Active Fuel Management temporarily deactivates four of the cylinders and seamlessly
reactivates them when the driver demands full power. When cylinders are deactivated, the
engine’s pumping work is reduced, which translates into real-world fuel economy improvements.
The transition takes less than 20 milliseconds and is virtually imperceptible.
The key to AFM’s efficiency and seamless operation is a set of two-stage hydraulic valve lifters,
which allows the lifters of deactivated cylinders to operate without actuating the valves. In
engineering terms, this allows the working cylinders to achieve better thermal, volumetric and
mechanical efficiency and lowering cyclical combustion variation from cylinder to cylinder. As a
result, AFM delivers better fuel economy and lower operating costs. The only mechanical
components required are special valve lifters for cylinders that are deactivated, and their control
system. Active Fuel Management relies on three primary components: Collapsible or “de-ac”
(deactivation) valve lifters, a Lifter Oil Manifold Assembly (LOMA) and the engine controller,
which determines when to deactivate cylinders.
Exhaust Manifolds
The LT4 exhaust manifolds are constructed of cast Austenitic Stainless Steel. The smooth flow
passages and equal length runner geometry were carefully developed using CFD analysis to
maximize the volumetric efficiency tuning of the exhaust gas flow.
LT4 exhaust manifold flow performance is equivalent to the LS7/LS9 tube and jacket design at
lower overall cost, optimized exhaust sound characteristics, and more consistent exhaust flow.
The manifolds are fitted with a pair of close-coupled catalytic converters that heat quickly,
achieving light-off temperature and closed-loop operations in seconds.
58X Ignition System
The Gen-V family uses an advanced 58X crankshaft position encoder to ensure that ignition
timing is accurate throughout its operating range. The 58X crankshaft ring and sensor provide
more immediate, accurate information on the crankshaft’s position during rotation. This allows
the engine control module to adjust ignition timing with greater precision, which optimizes
performance and economy. Engine starting is also more consistent in all operating conditions.
In conjunction with 58X crankshaft timing, the Gen-V applies the latest digital cam-timing
technology. The cam sensor is located in the front engine cover, and it reads a 4X sensor target
on the on the cam phaser's rotor which is attached to front end of the cam. The target ring has
four equally spaced segments that communicate the camshaft’s position more quickly and
accurately than previous systems with a single segment.
The dual 58X/4X measurement ensures extremely accurate timing for the life of the engine.
Moreover, it provides an effective backup system in the event one sensor fails.
Additional Features

Electronic Power Steering: All Gen-V engines have Electronic Power Steering and do
not incorporate a conventional, hydraulic power steering system in its accessory-drive
system. This enhances both performance and fuel efficiency.

Air Induction Humidity Sensor: This feature ensures optimal combustion efficiency,
regardless of the surrounding air’s humidity.

Coil-on-Plug Ignition: The Gen-V’s individual coil-near-plug ignition features advanced
coils that are compact and mounted on the rocker covers, although they are positioned
differently than on Gen-IV engine. An individual coil for each spark plug delivers
maximum voltage and consistent spark density, with no variation between cylinders.

Iridium-Tip Spark Plugs: The spark plugs have an iridium electrode tip and an iridium
core in the conductor, offering higher internal resistance while maintaining optimal spark
density over its useful life. The electrode design improves combustion efficiency.
E92 Engine Controller
Operation and performance of the Gen-V family is overseen by this next-generation engine
controller.
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