As Bear posted a wannabe Porsche Fiat 500, i remembered a lot of crazy builds. The good old 500 is a cult car, but the new one has already shown some potential as well.
This is probably the most you can squeeze out of the "standard" Fiat 500 Abarth. There is of course the Tributo series, that deliver 180bhp, but this one has 265
http://www.carscoops.com/2010/07/pogea- ... barth.html
Of course, if you want to go extreme, you fit in a Ferrari V8
http://www.autoguide.com/auto-news/2012 ... iller.html
Or even a Lamborghini V12 in an old school Fiat 500
http://www.dailymail.co.uk/news/article ... ngine.html