9ff GT9-R: 257 miles per hour (413.6 kilometers per hour)
The GT9-R, from the German Porsche tuner 9ff, was limited to just 20 cars. That might help explain why the company didn't make a big deal about trying to chase down any official records. Or maybe 9ff just didn't care, believing instead that this car speaks for itself. The GT9-R is basically a reconfigured Porsche 911, powered by a 4-liter, six-cylinder boxer engine that pushes the horsepower well into the four-figure range. Really. The 9ff GT-R has 1,120-horsepower.
Though the 9ff GT9-R became known for being one of the first street-legal race cars to cross the 400-kilometer-per-hour threshold, and it was soon demonstrated that the car could actually go quite a bit faster than the equivalent 248.5 miles per hour -- but that accomplishment didn't result in fame and fortune. Instead, 9ff filed for bankruptcy in late 2013, so it's unlikely they'll be churning out any more monsters, Porsche-based or otherwise.