Oemmedi Meccanica has built probably the craziest Fiat 500 on Earth. Sure this is more of an engine mashup than a true engine swap but something like this deserves attention. This Fiat has had two previous engine swaps; the first being a 3.2 L Porsche flat-six and the next was a 3.0 L Ferrari V8. The creator increased the displacement and number of cylinders again. The small car is now powered by a 6.2L V12 from a Lamborghini Murcielago.
Source: Yahoo Autos, Jalopnik, and Motor1 Italia