The E39 M5 in the post mentioned being upgraded with an ESS supercharger kit which adds a lot more power to the engine. This kind of upgrade can boost the car’s horsepower by 150 or more.

The kit comes with a comprehensive engine tuning package including a supercharger for the original 3.7-litre V6, pushing power beyond the 500hp (373kW) mark. Stillen has been around for a while ...