Why did the Daimler-Benz DB 605 compression ratio vary between cylinder banks?
The 605 (601E above) used a "wild" valve timing. This valve overlap would start letting in the air/fuel mixture, while the exhaust valve was still open. So the intake would help push out the exhaust. This hurts the low RPM performance, so a special low-speed intake was also added.*

This overlap, the rotation direction, the compressor (supercharger) being closer to the left bank, are some of the reasons that resulted in the right bank having a lower compression ratio than the left. This affected the 603 and 605, but not the 601 because it didn't have such a wild timing overlap.**

But isn't compression ratio constant due to the fixed volume (a reply to a comment):

No, dynamic compression ratio is a thing that is affected by valve timing. An example (not 605 related) is given as:


  However: intake valve closure (sealing the cylinder) always takes place after BDC (bottom dead centre), which may cause some of the intake charge to be compressed backwards out of the cylinder by the rising piston at very low speeds (...)




* enginehistory.org

** ww2aircraft.net (translated from another link)