Originally Posted by aajami
BMW created the S65 by lopping off two cylinders from the S85, so why wouldn't they create a new block by implementing the same process on the S63?
They wouldn't do that because they had designed the S85 from the beginning to share its architecture with the S65 V8. The design of the engines and the shared cost structure was planned from the outset (although there are many differences between the two as well). The S63 and S63Tu, on the other hand, are essentially evolutions of the N63 regular series engine. I am with mapezzul on this one: when they are trying to improve profitability of the M Division, it makes no sense to go spending a ton of money trying to chase down a high performance V6 from the bones of a V8 architecture.
It would be kind of like them saying: "Hey guys instead of basing the M5 on the 5 series, lets base it on the F30 3 series, but blown up just a little bit in every dimension. This way, we can justify it better to M enthusiasts, even though it cost a lot more money to do it this way with no substantial, tangible benefit."