Docstoc

1 GM Powertrain (DOC download)

Document Sample
1 GM Powertrain (DOC download) Powered By Docstoc
					2011 "LS7" 7.0L V-8 ( LS7 )
7.0L CORVETTE V-8 (LS7) CAR ENGINE

New content

The enhanced 2011 LS7 7.0L lubrication system now uses the LS9 engine oil pan mounted oil
cooler. This coolant-to-oil oil cooler provides improved heat exchange capability which enables
more robust higher oil pressures during aggressive driving conditions.


Carryover features and benefits from 2010 model year

Overview
The 7.0L LS7 V8 is a bundle of superlatives: the most powerful production small-block V8 ever;
ditto the highest operating speed (rpm) ever; more torque than the high-performance V10 in
Porsche's Carrera GT or the V12 in Ferarri's 575M Maranello.

In an emotional sense, the LS7 connects the Corvette to its glorious past. Its 7.0-liter
displacement translates to 427 cubic inches, identical to one of the most revered engines in
racing and automotive lore-the original 427 Corvette big block. In a cold factual sense, the LS7
delivers a combination of attributes few engines-perhaps no engine--can match. It combines
very high horsepower, torque and world-class race track performance with refined, tractable,
rock steady operation on the street. Measured by mass, package size, performance or cost to
the customer, the LS7 V8 meets or surpasses the best overhead cam V8s in the world.

The starting point for the LS7 was the first engine built for the fifth-generation Corvette-the Gen
IV 6.0L LS2 V8. The LS2, in turn, had built on two milestone engines: the LS1 and LS6 V8s
developed for the C4 Corvette. Those Gen III engines had introduced a host of leading-edge
technologies to the grand tradition of the Chevrolet small block V8, starting with all-aluminum
construction, a thermoplastic intake manifold and drive-by-wire electronic throttle.

The LS7 development team applied a number of design elements and technologies introduced
and validated in the Corvette C5R road-racing program. To increase displacement, both bore
and stroke were increased compared to the LS2--104.8 mm and 101.6 mm, respectively, versus
101.6 mm and 92.0 mm of the 6.0L Corvette V8. As a result, the LS7's cast iron cylinder sleeves
are pressed into, rather than cast in, the aluminum engine block. LS7 pistons feature tapered
wrist pins to reduced weight. The piston rings are anodized to reduce blow-by and friction, while
the skirts are coated with a polymer material to limit bore scuffing and reduce noise. Titanium
connecting rods weigh 464 grams each or 27 percent less than the rods in the 6.0L LS2. The
lighter rods reduce the pressure on the rod end bearings and the main bearings, and allow the
bearings to be optimally sized for the least amount of friction. Six-bolt, doweled-in, forged steel
main bearing caps hold the balanced crankshaft in place and reduce crank flex. The weight
trimming, friction-reducing features in the LS7's bottom end lower reciprocating mass and
contribute to its 500-rprm maximum speed increase (7100 rpm fuel shut-off) compared to the
LS2.

The old hot-rodding axiom about air in, air out applies to the LS7. The extra displacement would
mean little in terms of horsepower if the engine could not draw in and then expel enough air to
take advantage. To that end the LS7 is fitted with all-new cylinder heads. Fully CNC-machined
intake and exhaust ports and combustion chambers reduce flow restrictions; the high machining
consistency also allows a higher compression ratio. Valve angles are decreased to 12 degrees,
compared to 15 degrees in the 6.0L LS2. The rocker arm ratio increases from 1.7:1 to 1.8:1
ratio. Low-friction hydraulic roller lifters actuate the valves, operated by the highest lift cam in
Powertrain's production vehicle inventory. Valves are larger and taller than those in the LS2,
with titanium intake valves and hollow stem, sodium-filled exhaust valves to optimize heat
transfer away from the valve face.

The intake system benefits from similar part-by-part review and refinement. The result is a 20-
percent decrease in flow restriction compared to the LS2. The LS7 intake manifold is three-
piece friction-welded composite, with large straight intake runners designed to maintain fast
airflow velocity. Maximum air-flow volume increases 18 percent over the LS2. The filter element
is supplied by Donaldson Company, Inc., known for high-performance racing filters.

The exhaust manifolds are stainless steel-slipperier and lighter than cast iron-hydroformed into
a unique 4-into-1 collector designed to maximize flow. Exhaust pipes on the LS7-equipped
Corvette Z06 are three-inches in diameter, compared to the 2.5-inch pipes on Corvettes built
with the 6.0L LS2. The LS7 mufflers contain a butterfly valve that opens at high exhaust flow
levels and by-passes the "tri-flow" S-shaped path the exhaust gases normally follow. This
reduces exhaust restriction, yet allows the Corvette Z06 to hum at a more muted burble during
part-throttle operation (or typical back-and-forth driving).

To ensure the 7.0L LS7 V8 operates at peak, low-friction efficiency, and to promote durability
during extended high-rpm use under high cornering loads, the engine is equipped with a racing-
style dry sump lubrication system and dual-gerotor oil pump. The dry sump system scavenges
engine oil from the engine utilizing the first stage of the dual stage gerotor oil pump. Oil and air
are collected from the bottom of the engine oil pan and then transported to the external engine
compartment mounted reservoir for conditioning and storage. Oil is transported to the top of the
tank through an internal scavenge return tube, where it is tangentially spilled out on a spiral-
shaped internal baffle. When the aerated oil from the engine contacts the internal surfaces of
the tank, crankcase gasses and air which are entrained in the oil are separated out. These
gasses are directed by the PCV system through a series of baffles and tubes back to the
crankcase and into the combustion chamber to be burned. The de-aerated oil is directed down
the walls of the tank to collect in the 10 quart reservoir, conditioned and ready for use. The
second stage of the dual stage gerotor pump then draws the conditioned oil from the tank and
pressurizes it, feeding it to the engine via the oil filter and oil cooler. The routing of the engine
oil to and from the dry sump reservoir also provides the benefit of passive oil cooling.

If its capability and high-speed potential seem to suggest otherwise, the LS7 nonetheless
requires minimal maintenance. Its advanced iridium-core spark plugs and Dexcool coolant are
validated to 100,000 miles of operation, with the same level of performance at 90,000 miles as
they deliver at 10,0000. The LS7 also features an oil-level sensor and GM's advanced Oil Life
System. This technology measures stress on the engine and calculates oil life based on real-
world use rather than a predetermined mileage interval. It eliminates unnecessary oil changes in
vehicles that are driven in light duty conditions.

For all the improvements and advanced technologies built into the 7.0L LS7 V8, the bottom line
still counts most. This is an ultra-high performance engine, with capabilities suited to one of the
best performing sports cars in the world. It takes a back seat to no V8, blurring the line between
overhead-cam and pushrod-actuated technology to the point where the distinction is
meaningless-except for the relative cost advantages the pushrod engine delivers to both
corporation and customer.

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:3
posted:2/11/2012
language:
pages:2