The LS6 is a higher-output version of GM’s LS1 engine and retains the same capacity.

The LS6 shares its basic block architecture with the GM LS1 engine, but other changes were made to the design such as windows cast into the block between cylinders, improved main web strength and bay to bay breathing, an intake manifold and MAF-sensor with higher flow, a camshaft with higher lift and more duration, a higher compression ratio, sodium filled valves, and a revised oiling system better suited to high lateral acceleration.

via wikipedia