When you look at cars like the 3000GT VR-4, 300ZX turbo, Mazda RX7 turbo, and Toyota Supra turbo (all since extinct by the way) they all have dual turbos. In the 3000GT and 300ZX you get the boost of both turbos at the same time. However, the RX7 and Supra have a sequential turbo system in which you get the first turbo intially and the second one further up the RPM range.... Which is better...?? I have driven the Toyota Supra turbo and have noticed that second surge around 4000 RPM's or so. I'm not sure about the S4, but when my friend drives his I don't notice that the individual turbos are activated sequentially (due to the linear power deliver...... Just a thought for you guys to ponder. Personally I liked the turbo system of the 300ZX more than I did the Supra (with the boom.. BOOM)..