I've clarified my comment about SIDI being similar to a diesel. Both diesels and SIDI engines directly inject fuel into the combustion chamber. I've added text that diesels rely on high compression ratios to auto-ignite the fuel-air mixture, whereas SIDI motors still use a spark plug.
A reader also brought to my attention that Honda uses cylinder deactivation in its 3.5-liter SOHC V6 engine. My point - and it should have been stated more clearly - is that cylinder deactivation hasn't seen fuel economy returns worth the investment necessary for a full size truck's V8 - or else Toyota and Ford would have offered this in their OHC V8s already.
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This is the toughest story I've written.
On Friday afternoon I watched the newswires and Wall Street Journal break information about GM's future product plans that were revealed in the "White Book" agreement between GM and the UAW settling last week's strike.
One of the items that caught my attention was the name of GM's next full size truck platform, C3XX. So, I went and did some more background searching on the 'C3XX' identifier, using Google.
To my surprise a second, internal UAW-GM document appeared in Google's search results. The document can be found on the Future of the Union website and Google's publicly available search cache.
On Friday the document ranked much higher in the search results, before the "White Book" news containing the 'C3XX' term at more popular websites moved up in Google's page rankings.
The information about what's contained in that document is in the story below.
After wrestling with this decision, and consulting with several colleagues, I've decided to publish this story because I believe it's relevant to the "White Book" news and GM's current state of affairs with the UAW.
- M.L.
A document found online (using Google) at the Future of the Union website suggests that General Motors is preparing to substantially overhaul the engine lineup used in its next generation full size trucks.
Future of the Union has published an internal memorandum of understanding that contains detailed information about contract negotiations that took place in June 2007 among the United Auto Worker (UAW) union, General Motors (GM), and GM?s largest supplier, Delphi.
The document contains GM?s future product commitments to UAW-represented employees at Delphi, similar to the future product timelines that emerged from the recent strike settlement contract between GM and the UAW.
Most notable are the powertrain components that Delphi is expected to supply for use in the C3XX truck program, starting in 2011. The C3XX platform will replace the current GMT 900 architecture that underpins the Chevrolet Silverado and GMC Sierra full size pickups.
According to the document, C3XX pickups will feature a new 'Gen V' 6.2-liter dual overhead cam (DOHC) V8 engine - a major departure from GM's traditional overhead valve (OHV) pushrod engine design used in its trucks, like the ?Gen IV? 403-horsepower / 417 lb-feet L92 6.2-liter V8 under the hood of the GMC Sierra Denali. The only DOHC V8 GM currently offers is Cadillac?s 4.6-liter Northstar engine.
The Gen V 6.2 motor will use variable valve timing (VVT) like the Gen IV 6.2, but the use of dual overhead cams holds the promise of four valves per cylinder instead of the current two valves, for better intake and exhaust flow and increased power. This is a similar setup to the 5.7-liter i-Force V8 used in the Toyota Tundra, but the Gen V 6.2 will also offer GM's active fuel management (AFM) system. AFM shuts down half the cylinders during steady state running for improved fuel economy ? a feature not currently available for the i-Force. Up until this point, it?s been conventional wisdom that implementing cylinder deactivation on OHC engines is impractical for reasons of cost and complexity.
Pushrod engines won?t be disappearing entirely from GM?s truck line. A new ?Gen V? OHV V8 will replace the current 320-hp / 340 lb-feet 5.3-liter V8. Apparently the final displacement hasn?t been determined yet, because it?s referred to as 5X.
The new 5X gasoline engine will feature spark ignition direct injection (SIDI), similar to a diesel's fuel injection setup but still using a spark plug to ignite the fuel instead of diesel's high compression ratio that causes the fuel air mixture to auto-ignite. SIDI places the fuel injector right inside the combustion chamber, so fuel can be directly mixed with air entering the chamber during the intake stroke instead of before it enters the chamber, like in a conventional multi-port fuel injected gas engine. This approach enables a leaner burn of the fuel at higher compression ratios than current gas engines, resulting in greater fuel economy, cleaner emissions, and more power.
Initial production of both engines is slated to start in 2011 with full production in 2012.
Of course, it's possible that because this information is still approximately three years out in time, plans detailed in this document for the full size truck powertrains could still change.
Contacted for comment, a GM spokesperson told PickupTruck.com that GM doesn't make statements about documents like this.
There was no phone number or names listed to contact the Future of the Union website for comment.
http://www.pickuptruck.com/html/news/gm/uaw/futureunionuaw.html
I kid, I kid! 
with chevy version of mad V-tak and redline around 9k..