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, t.
1958 F.R Tg 500 'Tiger' Microcar The Tiger, produced by the Fahrzeug und Maschinenbau Regensburg in Germany, went from zero to 60 mph in 28 seconds, with a top speed of 78 mph. With a horsepower engine and four wheels.