LS1 AFM

[bytor]

Learning about all the technology and systems on the new C7 vette. The active fuel management system is an interesting one. Under certain load conditions, it disables 4 cylinders and basically converts a V8 to a V4. This only happens when in Eco mode. I understand the system operation basics and how GM uses oil pressure do disable the valve lifters to inactivate the 4 cylinders, nothing new. But what I don’t understand is if the intake and exhaust valves are closed on the deactivated cylinders, wouldn’t the piston be fighting against compressed air or vacuum? It would seem there would need to be some way to ‘vent’ the disabled cylinders. Am I missing something?

http://media.chevrolet.com/media/us...10/typeId/c/currentChannelId/Most Recent.html

 

[Grumpy]

 

[bytor]

Any thoughts on this? It would seem if the intake and exhaust valves are both closed and depending on where the piston is in the stroke, you would be fighting pressure/compression approaching TDC or fighting a vacuum as the piston goes to BDC. I would imagine there has to be some cylinder leakage or venting when in AFM mode. Interesting stuff...

 

[Grumpy]

I can see how there would be both pressure and vacuum as you stated but Id bet that was considered and, it might be that the exhaust valve is not fully seated on the DE-activated cylinders
but in any case it obviously has been tested and proved beneficial or they would never include or offer it as an option