a good engine a two speed would let the RS4 go 60mph, but due to poor suspension geometry, and lack of tuning ability - it would constantly spin out and be impossible to control. IAlong with that, the drivetrain in the RS4 is designed to handle sport engines, not the hi power race engines that would be required, gears would melt, driveshafts would break, ect....if you stuck a Formula 1 engine into a Hyundai Accent, would it go 150mph? probably, but it would either disinegrate the drivetrain, or be impossible to control, right?