Complementing the larger-port design of the heads are commensurately sized valves. The intake valve size alone increases from 2.00 inches (50.8 mm) to 2.16 inches (55 mm)-an increase of nearly 9 percent. The intake valves feature lightweight hollow stems, which enable the engine's 6,600-rpm capability. The exhaust valves also are large, measuring 1.60 inches (40.4 mm) in diameter.
To accommodate the engine's large valves and enable more direct intake-port flow, the intake-side rocker arms are offset 6 mm between the valve tip and the pushrod. Actuating the valves is a new camshaft, with intake-side lobes providing more than a 5-percent increase in lift, from 0.521 inch to 0.551 inch (13.25 mm to 14 mm). Exhaust-valve lift remains unchanged from the LS2. The camshaft timing was revised to optimize performance with the higher-lift intake cam profile.
High-Flow Intake Manifold
Ensuring the cylinder heads receive all the air they can handle falls to a new, acoustically tuned intake manifold. The composite design is manufactured with a "lost core" process that improves runner-to-runner variation and reduces airflow losses. An acoustic foam material is used to reduce radiated engine noise; it is sandwiched between the outer top of the manifold and an additional "skull cap" acoustic shell. new beauty covers atop the engine shield the rocker covers and also feature a noise-reducing, acoustically tuned insert to provide a more refined engine sound.
New Optional Dual-Mode Exhaust System
Optional on '08 coupe and convertible models is a new, two-mode performance exhaust system. Similar in design and function to the system used on the Z06, the dual-mode exhaust uses vacuum-actuated outlet valves, which control engine noise during low-load operation, but open for maximum performance during high-load operation. It is not identical to the Z06 system; the coupe/convertible uses a 2.5-inch-diameter exhaust, while the Z06 uses a 3-inch system.
With the new, dual-mode performance exhaust, power output for the coupe and convertible rises from 430 hp (321 kW) and 424 lb-ft of torque (575 Nm) to 436 horses (325 kW) and 428 lb-ft (580 Nm). This system gives the Corvette a more aggressive exhaust sound character that will appeal to performance enthusiasts.
Improved Manual Transmission Shift Effort
The shifting efforts for both the six-speed manual transmission and paddle-shift, six-speed automatic transmission have been improved in the '08 Corvette models. The manual transmission shifting improvements include a more positive and direct feel during gear changes, with better gate-to-gate location.
Quicker Shift Times On Paddle-Shift Six-Speed Automatic
The six-speed, paddle-shift automatic transmission on the coupe and the convertible is improved with new hardware and a new controller calibration that delivers quicker shifts. This change bolsters the feeling of performance and driver control when using the shifting paddles.
Also new for '08 models is the availability of the 2.73 performance axle ratio with the automatic transmission. It is included with the Z51 package.
Improved Steering Feel
The Corvette's precise rack-and-pinion steering system has been revised to provide improved feel at all speeds. The revisions are due to a new, premium machining process of the system's internal components, a new, stiffer intermediate shaft, and controller calibration changes.