[woderd]

Does anyone think BMW will have the technology to put a v8 under the hood then flip a switch to only run on 4 cylinders to save gas?

I heard of another manufacture already doing this but cant remember what one.

[MophoMan]

The zr-1 has a valet mode which does that I think.

[OzDriver]

Originally Posted by woderd

Does anyone think BMW will have the technology to put a v8 under the hood then flip a switch to only run on 4 cylinders to save gas?

I heard of another manufacture already doing this but cant remember what one.

The Honda Odessy and Chrysler 300C have a variable displacement system. I think M-B also did it on their V12 engines.

BMWs have a low power Transport Mode for shipping new cars, but I think it's n electronic limiter rather than shutting down cylinders.

[HighlandPete]

Originally Posted by woderd

Does anyone think BMW will have the technology to put a v8 under the hood then flip a switch to only run on 4 cylinders to save gas?

I heard of another manufacture already doing this but cant remember what one.

I was reading an article the other evening where BMW argue the efficiency using their valvetronic system, is similar to cylinder switch off.

They illustrate it like "dimming all lights" rather than switching off half of the bright ones.

Makes some sense, and I'm sure BMW will have tried both methods. If efficiency is close, it would be reasonable to stay with valvetronic and make advances with that as the core technology.

HighlandPete

[Douggie]

With the way things are heading, the 550i will eventually just have 4 cylinders with 3-4 multi scroll-turbos. No need any switches.

http://f20.1addicts.com/forums/showthread.php?t=789117

[Terpinator]

Audi's new 4.0L V8 used in the S6, S7 and S8 has cylinder deactivation, where they run on 4 cylinders when under light load. They have to use active sound management and active engine dampers to quell unwanted vibrations and noise when operating on 4 cylinders.

I'll take BMWs valvetronic approach.

[The X Men]

BMW's valvetronic system is similar with Audi's Valvelift System, they are both basically varible valve system, invented by Honda years ago. The S6's cylinder deactivation works together with the Valvelift System to increase fuel efficency. Thats one of the reason why the S6 gets 17/27 MPG while the 550xi only get 16/24 MPG.

[KoenG]

The loss of efficiency with a gasoline engine is caused by the need to have a stochiometric balance between air and fuell. So when you want to run at none full throttle, you cannot fill the entire cilinder with air. To reduce the inflow of air, a "normal" car just closes down the air inflow over the entire inlet stroke down. The gasoline paradox is: less output == more losses!

Assume you're half throttle, the cilinder only receives a half doses of air by "choking" the inlet, generating an underpressure of 0,5 bar over the entire inlet stroke down. Valvetronic allows 0 bar underpressure for the first half of the strokedown, and then closes entirely the inlet valve, building the underpressure from 0 uptil 0,5 at the end of the inlet stroke. This way the losses are divided by 4! Since the average underpressure during inlet stroke is only 0,125bar!

Cilinder shut down, avoids that the active part of the engine is running in comfort zone where the pump losses are unacceptable high. Each of the active 4 cilinders will receive double the air inflow as when running on 8 cil. This mechanism HALFS the pump losses.

Combining this technology, would povide a mechanism to reduce the pump losses with a factor 8, but only at very mild regimes. When you would demand more then 25% of the output (torque that is, not power), the cilinder switch out should stop and only valvetronic remains active. I guess this is only usefull on very long high road trips with moderate speed on a flat high road that is.

[KoenG]

Originally Posted by The X Men

BMW's valvetronic system is similar with Audi's Valvelift System, they are both basically varible valve system, invented by Honda years ago. The S6's cylinder deactivation works together with the Valvelift System to increase fuel efficency. Thats one of the reason why the S6 gets 17/27 MPG while the 550xi only get 16/24 MPG.

Watch out, the 650i Xdrive has more output and consumes less fuell, without cilinder shut down! S6=225g CO² and 650ix=215g CO² so the consumption is less with only Valvetronic. The 550i will get this update also this year so the lagging position is only temporal.

Audi's Valvelift is more VANOS+VTEC I guess and not a functional equivalent of valvetronic.

[The X Men]

Originally Posted by KoenG

Watch out, the 650i Xdrive has more output and consumes less fuell, without cilinder shut down! S6=225g CO² and 650ix=215g CO² so the consumption is less with only Valvetronic. The 550i will get this update also this year so the lagging position is only temporal.

Hmmm, the US spec 2013 650xi coupe get the same MPG as the 550i, 16/24 MPG.