This Audi is not what it looks like. It’s badged an S4 but it’s the test mule for the new RS4, spotted near the Nurburgring circuit. The extended wheel arches are straight from the RS parts bin. Another thing, the RS4 will use the S4’S 3.0-litre V6, only it will come with an electric turbocharger to boost power to around 360kW. That’s around 30kW more than the old 4.2-litre V8. Audi’s main technical man Dr Ulrich Hackenberg has said the electric booster provides instant torque lower in the rev range and is more efficient than twin sequential turbochargers in minimizing turbo lag. It is powered by batteries which are charged through a generator that recoups lost energy under braking. The downside is the electric set-up is more expensive than twin boosters, the reason why it is likely to be used only on top-end performance Audis.