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Old 03-16-2007, 08:34 AM   #10
LSxcellent
 
Drives: MINI Cooper S
Join Date: Jan 2007
Location: Boston, MA
Posts: 284
And from the GM Media Online site:

"Variable valve timing

Variable valve timing (VVT) is a standard feature on 6.0L and 6.2L engines; it helps optimize camshaft timing to improve low-rpm torque and high-rpm horsepower. The introduction of variable valve timing through the unique dual-equal cam phaser is the industry’s first application of VVT on a mass-produced V-8 cam-in-block engine. The unique dual-equal phaser adjusts the camshaft timing at the same rate for both the intake and exhaust valves.

The system incorporates a vane-type camshaft phaser that changes the angular orientation of the camshaft, thereby adjusting the timing of the intake and exhaust valves to optimize performance and economy, and help lower emissions. It offers infinitely variable valve timing in relation to the crankshaft. The cam phaser vane is attached to the camshaft on the front journal. As driving conditions warrant, the cam phaser system can reduce ignition timing at higher rpm levels to increase power. At lower rpm levels, torque is enhanced with increased timing.

This cam phaser feature was pioneered by GM and introduced on the new 3.5L and 3.9L V-6 engines in 2005 – a first for the use of variable valve timing on a cam-in-block engine design. As driving conditions warrant, the cam phasing system can reduce ignition timing at higher rpm levels to increase power. At lower rpm levels, torque is enhanced with increased timing.

Precise camshaft timing is the key to the variable valve timing system’s capability to optimize performance. Like the 58X ignition system, cam phasing is directed by the E38 ECM. It relies on data from a camshaft position sensor – a target ring with four equally spaced segments – that communicates the camshaft’s position quicker and more accurately than previous systems that used just a single segment. Also, a leaf spring-type tensioner is used on the timing chain to ensure precise tension.

The aluminum-block 6.0L version uses variable valve timing in conjunction with Displacement On Demand technology to bolster fuel economy. With cam phasing, Displacement On Demand technology allows the engine to run longer in fuel-saving four-cylinder mode, while producing instant V-8 power and response as soon as the driver calls for it.
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~LSx
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