The Radical range is a full production road legal car in the UK. The base engine is a Suzuki Hayabusa 1300cc engine and they also do a 1500cc version and 1500cc turbo. The SR8 has a new engine they developped themselves which is basically 2 Hayabusa engines turned into a V8, about 2600cc and a redline of 12,000RPM!!! There is a Radical Australia but unfortunately they are not road legal.
I am fortunate enough to have experienced one of their cars on the race circuit (the SR3 2 seat version) and even with road tyres and 2 people on board it will pull 2g in the corners and destroy machinary worth many times more!