New Corvette Engine Shatters Previous OHV RPM Limits

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PONTIAC, Mich., Feb. 8 /PRNewswire/ -- GM engineers have achieved a feat
many speculated was not possible. The new LS7 7.0-liter OHV (overhead valve)
V-8 engine for the 2006 ZO6 Corvette will not only achieve 500 horsepower but
will be capable of running up to 7100 rpm. The previous limit was 6600 rpm in
the 6.0-liter LS2.
With this new engine GM is showing multi-valve overhead cam performance is
achievable with a two-valve cam-in-block engine. For the new ZO6, higher rpm
allows the driver to remain in first gear to just over 60 mph, contributes to
higher top speed and improves overall vehicle performance. The LS7 is one of
the first automotive OHV production engines in the industry capable of over
7000 rpm.
The new ZO6's sub four-second 0-60 mph time is achieved in part by the
extended rpm range and the ability to remain in first gear past 60 mph. The
over-190 top speed of the ZO6 is partially due to the speed capability of the
engine. As aerodynamic drag becomes a factor at higher speeds, the capability
to run higher rpm allows the transmission to be run in a lower gear generating
more effective torque at the rear wheels. Also, having the ability to shift
all gears at higher speeds improves elapsed times whether on a road course or
drag strip.
"For a production engine to run at this high of an rpm blurs the lines
even more between OHV and OHC (overhead cam) design," said Dave Muscaro,
assistant chief engineer for small block engines. "We took a complete systems
approach to achieve the high rpm. We have a tight valvetrain design along
with some race-inspired materials for the reciprocating components like
titanium intake valves and connecting rods."
OHV engines use pushrods to activate the valves via rocker arms, whereas
with OHC engines the valves are typically actuated directly via finger
followers. The extra mechanical movement and weight of the components of an
OHV valvetrain present challenges to higher rpm. The LS7 design and use of
lightweight, stiff components, along with GM's economy of scale, make higher
rpm obtainable in a production OHV engine.
"The new LS7 cylinder head gave us the opportunity to design a new high-
revving valvetrain," said Jim Hicks, LS7 valvetrain design engineer. "The new
valvetrain had to be as stiff and light as possible to assist meeting the
engine's aggressive performance targets without compromising idle quality and
low emissions. Stiffness is increased with larger diameter pushrods and
rocker arms optimized through extensive finite element analysis."
The LS7's 1.8:1 rocker arm ratio and titanium intake valves contribute to
a lower effective mass (compared to the LS2 base Corvette engine) in spite of
larger and stiffer valvetrain hardware. Idle quality and emissions
performance is achieved with the help of a more aggressive cam that provides

more lift and duration while still keeping overlap area to a minimum.
"We consulted with our Motorsports group on numerous design aspects of the
cylinder head design," said Hicks. "We adopted some of the latest ideas that
have been successful in the Nextel Cup and the American Le Mans Series
including valve centerline positions, valve angles, valve sizes and rocker arm
ratio."
Due to the relatively large bore and stroke (104.8 x 101.6mm) of the LS7,
light weight pistons, piston pins, titanium rods and a steel crankshaft are
also used to achieve extended rpm. The flat top pistons with race-ready valve
reliefs are 482 grams each and use a shortened lightweight piston pin. Each
forged titanium rod weighs only 464 grams which is almost 30 percent less than
each rod in the LS2. The forged steel crankshaft is stronger, stiffer and
designed to handle high-speed loads.
General Motors Corp. (NYSE: GM), the world's largest automaker, has been
the global industry sales leader since 1931. Founded in 1908, GM today
employs about 324,000 people around the world. It has manufacturing
operations in 32 countries and its vehicles are sold in 200 countries. In
2004, GM sold nearly 9 million cars and trucks globally, up 4 percent and the
second-highest total in the company's history. GM's global headquarters are
at the GM Renaissance Center in Detroit. More information on GM can be found
at http://www.gm.com .
 

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