John317: Some people might be trying to differentiate the 05s from the earlier Gen III models because the 05s have the new "CAN" ("Controller Area Network") data bus, which has a far higher throughput capacity and quicker response time than the older data bus used up to now. That CAN bus is making it VERY difficult for aftermarket companies to reverse engineer the PCM programming, and many things posible on the earlier Gen III engines are not yet possible on these latest 05 variants.
GM is sprt of encouraging the talk about "Gen IV" as they ARE inded HEADED there.
What is happening is that GM is slowing phasing in certain "Generation IV" features as it prepares to offer a line of engines that will support "displacement on demand". When all those features are in production, THEN there will actually be a "Gen IV" line of engines.
These will include a number of features needed to support the flagship feature and objective: displacement on demand (DOD). These required features include:
- Faster bus (the CAN bus) needed to respond quickly enough to support DOD
- New oil galleries in the block (already being phased in) needed with DOD, because some cylinders not firing will create a different thermal and lubrication environment
- Knock sensors relocated from engine valley to external locations, to make them less sensitive to sounds associated with DOD, as otherwise they would trigger the PCM to retard the ignition timing when NOT actually required or desired
- Camshaft position sensor relocated from back to front of engine (reason not specified)
A true Gen IV engine will have the defining feature: displacement on demand. Everything else is just prep work for that, and done in the interests of standardized componentry (even for variants that don't need the individual features).
The DOD is needed to make a quantum jump in fuel mileage. Hopefully, it will more reliable than the unsuccessful Cadillac effort of years ago.
Thanks Jim, I knew that you would have a well researched answer. I remember the last attempt by GM. I wonder why they don't try some of these ideas in fleet applications prior to foisting them on an loyal customer base?
John317: I used to be a VP of Operations in a previous career, and know how really, really good intentions sometimes get sabotaged by unforseen events.
I have learned to try to not condemn good faith efforts that create problems, as long as the folks involved act honorably to alleviate the undesirable repercussions.
I could tell you horror stories, like the self-propelled commercial walk behind lawnmower that worked great EXCEPT the wrong engine part number was specified by the engineer so it rolled BACKWARDS, attacking the quality manager. when it was started up for quality testing. The engineer had told us that he had built and tested a prototype. The QC manager was understandably pissed.
Then there was the high speed tampon packaging machine that fired tampons all over the factory during its unsuccessful demo run for the client that commissioned it.