Quote:
Originally Posted by pete c
There are other things done with the idle speed, fueling, spark advance, etc. in concert with the cylinder cut out but the main function that makes the limp home system work is the cylinder cut out. Remember, the valves are still operating so the cylinder still pumps air thru it...making it an internally air cooled engine when in limp home mode. This is often confused with the DOD (displacement on demand) system upcoming on GM engines and the older V-8-6-4 system on the 81 Cadillacs. They are not the same as the Northstar limp home mode. In DOD the valves are actually disabled so that they stay closed to disable the cylinder. Just turning off the fuel to disable a cylinder causes huge pumping losses that are immediately evident trying to drive the car. With only 4 cylinders running and 4 dead but still pumping the engine has the net output of about 1.5 cylinders as much of the power goes into the pumping loss of the dead 4 cylinders. In DOD, the gases trapped in the cylinder act as an air spring returning the power used to compress them to he piston on the down stroke.
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I wasn't trying to troll. Simply wondering the pros and cons, and if anyone had tried it. Pete, this was exactly the answer I was looking for, so thank you.
I opened my membership a year and a half ago, but I admit I rarely spent any time on the forums. I apologize for not being able to sort through the pages (literally thousands of entries) on the subject to find my answers (amidst all the "can I just take the piston out and run it like that and get thousands of MPG?" threads.)
So FINALLY, after three and a half pages of scoffing and mocking the "retarded new guy who thinks he knows everything", I get two real answers. Thanks.