KresoF1:

First, just confirmed-new RS5 will get V8 100% for sure.

Downsizing... New S4 engine is pure example of that. Much, much lower CO2 emissions that S5 V8 engine.  Power is not the same 3.0TFSI is available in tow versions: 290ps(for A6) and 333ps(for S4 and engines are different in some way). S5 current 4.2 FSI is with 354ps little bit more powerfull.

Do not forget that both S4 and S5 are not aimed against M3 or C63 AMG.

V8 Na or TT or supercharged?

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V6, V8 or V10?