What happens when you have a race series with fairly open rules and the manufacturers get involved? You get what is arguably the most powerful road racing car ever. The Porsche 917/30 could put out around 1500HP when they turned the turbos all the way up. The car shown here is the 1973 championship winning car run by Roger Penske for Mark Donahue

Image credits: Hemmings.com, Caranddriver.com and douleclutch.com