Cylinder on demand

[JAMES]

I believe in the w12 the engine switched banks to keep the cats ect warm and effectively ran on 6 one side or the other. The v8 however has an actuator to also disengage the cam shaft from the valves. I presume this saves fuel as it is no longer using energy to lift the valve. However it seems mad to me not to have a release valve to allow the cylinders to run freely

[JAMES]

https://youtu.be/BiFXXmtSFhQ

[wildbore]

I believe in the w12 the engine switched banks to keep the cats ect warm and effectively ran on 6 one side or the other. The v8 however has an actuator to also disengage the cam shaft from the valves. I presume this saves fuel as it is no longer using energy to lift the valve. However it seems mad to me not to have a release valve to allow the cylinders to run freely

You can only let air out if there is sufficient room in the combustion chamber to have a valve that is open (or open the exhaust valve). Most modern engines have such tightly optimised combustion chamber spaces that there is no room for a valve that opens inwards into the combustion chamber, and engineering one that opens outwards would be an interesting technical challenge.

I am unsure, too, what the effect of "unburned" (i.e. oxygen-rich), cold air from the four non-running cylinders would have on the cats, turbos and sensors in the exhaust path if that is where the non-running cylinders were vented (via the exhaust valve).

[feeltheburn]

Good explanation here:

http://www.autopedia.co.uk/motoring-inf ... -explained

[JAMES]

It seems this is stage to of cod (w12 being stage one) so maybe stage 3 will see further technology and fuel improvement. Or maybe the introduction of electric motors will take over from investment in this

[alexrs6plus]

Wanted to resurrect an old thread for curiosity reasons as is in the same ball park with my question regarding running in and cod.

Audi do say to run it in and take it easy for the first 1000km, then next 500km start running higher revs so the pistons and the bores of the cylinders have time to bed in properly.
My theory is if you decide to do most of this running in period on motorway's or A roads, keeping the car at cruising speed and the cod activates for most of the time aren't those cylinders that have shut down not being run in properly?

Surely if Audi was so concerned about the running in period, they should have the cod deactivated for the first 1000km until all the bores are fully bedded in or am i having a blonde moment?

[feeltheburn]

All 8 pistons continue to move regardless of COD although granted the associate valves of the COD are not in operation. A good explanation of how it all works is here:

http://www.autopedia.co.uk/motoring-inf ... -explained

There are many many theories regarding running in, the most stated one being not to run at constant RPM for any prolonged period of time. Tyres and brakes also need to run in for a bit but 1000miles seems excessive to achieve this imo.

The whole point of running in is to let the engine components "bed in" essentially conforming to each other. There is much to be said for running the engine hard from the get go [once it is up to temperature of course]. The cylinders have a certain roughness when first honed and it is argued that the rings can be made to conform better with the cylinders if run hard while this roughness still exists. The roughness is supposed to last for the first 25-60 miles so delivery miles might mean the opportunity has already gone.

http://www.mototuneusa.com/break_in_secrets.htm

I am still under warranty so I of course followed the run in Advice from Audi I have also never used a drop of oil for the first 10,000miles and none for the current 3000miles!

[wildbore]

I am still under warranty so I of course followed the run in Advice from Audi I have also never used a drop of oil for the first 10,000miles and none for the current 3000miles!

I never added a drop of oil from new to the first service at 18000 miles. The indicator still showed that the level was spot-on when the service was done.

[alexrs6plus]

Ahh ok, that clears things up for me.
cheers

[framerob]

I've had a couple of maps on my rs6c7.
Latest one stage 1 MRC.
Switch it to the mpg bar and it goes green when I brake , but no "4 cylinder mode" text under the bar?

Ive seen it before for sure.

Also occasionally get the EML popping on
Drives perfectly.

Can anyone help?
Rob