I was going through my fitted options list generated from my VIN when I discovered I had option #479 (from 04.08.1997 CYLINDER CUT-OUT SYSTEM (ZAS))
Looking under the car when I had the secondary cats removed I can see that both centre exhaust sections don't meet at a central silencer box for the crossover point they instead go to a diverter valve. I take it that this valve is open when in "V8 mode" and closes when in "V4 mode". After the valve the exhaust splits to each branch exit and has two silencers before the tailpipe on both sides. I wondered why the car never sounded like a V8 until I got the engine over 4k revs!
Translated from the German Wikipedia:
The 5-liter version of the M 113 is available with cylinder shut-off available (ZAS). At low load and up to a speed of 3500 rpm the engine runs only with four cylinders. It will be shut down two cylinders each bank so that the remaining cylinders evenly spaced light (180 ° crank angle). Here also, the valves are closed. The rocker arms are for two parts, and the parts can be disconnected by a hydraulically actuated piston from each other. The ZAS improves engine efficiency by smaller throttle losses and higher effective compression, because the cylinders are filled better. The fuel consumption of the S 500 (220 series) is by ZAS reduced according to the manufacturer by 0.9 l/100km.
Looking under the car when I had the secondary cats removed I can see that both centre exhaust sections don't meet at a central silencer box for the crossover point they instead go to a diverter valve. I take it that this valve is open when in "V8 mode" and closes when in "V4 mode". After the valve the exhaust splits to each branch exit and has two silencers before the tailpipe on both sides. I wondered why the car never sounded like a V8 until I got the engine over 4k revs!
Translated from the German Wikipedia:
The 5-liter version of the M 113 is available with cylinder shut-off available (ZAS). At low load and up to a speed of 3500 rpm the engine runs only with four cylinders. It will be shut down two cylinders each bank so that the remaining cylinders evenly spaced light (180 ° crank angle). Here also, the valves are closed. The rocker arms are for two parts, and the parts can be disconnected by a hydraulically actuated piston from each other. The ZAS improves engine efficiency by smaller throttle losses and higher effective compression, because the cylinders are filled better. The fuel consumption of the S 500 (220 series) is by ZAS reduced according to the manufacturer by 0.9 l/100km.