Maybe a little info here........
GM
General Motors is putting $6.25 million (matched by the DOE) into research specifically exploring variable-valve actuation, two-stage-series sequential turbocharging, and advanced ignition strategies in its 4.5L diesel. GM's partners in this project (that began back in 2005) include FEV, TEAM Corporation, Mechadyne International, Eaton, and Mitsubishi. GM's development of high-efficiency, clean-combustion diesel engines began with a single-cylinder engine that featured fully flexible variable-valve actuation and the 4.5L V-8 with a simple variable-valve actuation mechanism. The difference is the former does not rely on a fixed mechanical camshaft to open and close the valves; instead, an electro-hydraulic valve has complete control over valve lift and timing. The fully flexible valved engine achieved Tier 2 Bin 5 NOx engine-out targets without aftertreatment, but it's a technology not quite ready for production. The new valvetrain on the 4.5L is called Switching Roller Finger Followers and includes a concentric intake camshaft and phaser, and a two-profile exhaust lobe. Benefits of this new system include internal EGR (in which exhaust gas is kept in the cylinder), late intake valve closing (in which the dynamic compression ratio can be changed from 16:1 to 14.75:1), and the ability to vary the lift of the exhaust valve. These abilities equal cleaner emissions and more fuel economy, since PCCI ignition strategies can be achieved under wider operating ranges.
Read more:
http://www.dieselpowermag.com/tech/...ord_and_gm_diesels/viewall.html#ixzz1ug1sjvjx