Displacement on Demand / AFM could use info 2

[ScottI2R]

Hi All,
I just rented a a new gm with the 3.9L with AFM. I would like some details on how this works in the valve and ignition systems. The transitions between 6 and 3 cylinder mode were not even noticable. Detailed links will work. I have found generalisations "solenoids on the lifters" on the web but nothing detailed. I understand the old 90 degree pushrod V8's and valve and ignition timing in engines that were all mechanical but I could use a lesson in today's stuff. Also, any details on electronically variable valve timing would be appreciated as well. This would make sense to me in an engine where the valves were driven directly by individual solenoids but in my engine experience 60-70's SBC and BBC's, variable valve timing was a prelude to timing chain failure.

Thank you in advance,
Scott

In a hundred years, it isn't going to matter anyway.

 

[tbuelna]

 

[dcasto]

http://en.wikipedia.org/wiki/Variable_valve_timing

http://www.fueleconomy.gov/feg/tech_engine_more.shtml

The VVT-L is the most advanced, not only variable valve timing, but also valve lift (exhaust area). This technology allows 190 HP out of 1.8 liters and yet you can get 30 MPG.

 

[DynoTuner]

So are both valves closed to shut off the cylinder? It doesn't seem feasible. I would think that they'd leave the exhaust valve alone and allow it to be opening normally all the time to relieve cylinder pressure.

 

[TurboXS]

I think the idea is to close both valves and the air trapped in the cylinder acts like a spring. Leaving a valve open probably means higher loss through pumping losses.

 

[ScottI2R]

Ah yes! Pictures (1000 words) and links to boot! Thank you thank you!
Guess it wouldn't work too well with solid lifters but we dont use them anymore. I miss the old engines that would lope and throw fits till about 3500 r's and then go nuts. Oh well, I miss .39 cents / gallon too.

Thanks again,
Scott

In a hundred years, it isn't going to matter anyway.

 

[IceStationZebra]

Someone has a variable timing/variable lift design that can eliminate the throttle plate. I think it is on a high end Mercedes Bend.

ICZ

 

[patprimmer]

I think it is the high end BMW. The inlet valve is actually a throttle if it limits air flow into the cylinder in a controlled fashion.

Regards

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[TStaples]

ICZ, and Pat,
It is BMW developed engine technology. It's called Valvetronic. I had it on my 2004 X5 4.4L, and I also have it on my new X5 4.8L. It makes for a nice efficiency improvement at part throttle (i.e. where engines spend 98-99% of their operating life.), and gobs of low end torque. I like torque! (spoken in Tim Allen, Binford 9000 style!)

Check Out:

http://www.bmwworld.com/technology/valvetronic.htm

-Tony Staples

http://www.tscombustion.com