I think it's the 9ff GT9. I does 0-200mph in 24 secs and has a top speed of 258mph.
1- It's a non-production limited modification of a Porsche only 20 to be made, if you count it you have to count modified race cars. 2- It is alleged to reach 254.14(9ff's site claims 409km/h) not 258 3- The SSC Ultima Aero TT has been recorded at 257 making it both fastest production and street legal vehicle. (Should be noted that the new models of the Aero could beat this speed with their lightened rotating mass) Once again is you want to know a biggest,fastest,smallest, most... type question go to http://en.wikipedia.org/wiki/List_of_automotive_superlatives There is a freaking list... This question is asked every couple days and people are still replying with the wrong answer.
Well, the question is what is the fastest car in the world, not what is the fastest production car in the world. I'm sorry for the 258 mph, it is not the true top speed but the speed Jan Fatthauer said it was able to do. So, if you count modified race cars, who is the fastest?