German car tuner AC Schnitzer jumped on the green movement and developed an interesting power tuning of a 3-series BMW using auto gas.

The AC Schnitzer GP3.10 Gas Powered 3-Series BMW runs on Liquified Petroleum Gas (LPG).
AC Schnitzer used the V10 engine of the current M5/M6 BMW cars as the bases for this project. AC Schnitzer generates 552 HP/406 kW and produces up to 540 Nm from that engine. The sprint to 100 km/h takes 4.5 seconds, and the 200 mark is passed after just 13.9 seconds.
LPG is not only cheaper than gasoline but produces around 15% less CO2 from the exhaust.
Of course driving this high powered beamer still isn't very sensible to the environment, maybe we can close a coal-fired power plant somewhere instead. Fast cars are just too much fun.
AC Schnitzer showed the GP3.10 BMW at the IAA 2007.
More details on the AC Schnitzer site.