The Super Rocket Start is something that is only possible in Mario Kart 7, it works similar to a normal Rocket Start except for the fact that it lasts twice as long which is really handy for taking an early lead. To do it you simply have to start accelerating as the number 2 stops spinning, get it just right and the boost last longer. But if you're even just a nanosecond to soon, there will be you're kart spinning out. It's tricky to master but totally worth it. Here is a youtube video showing you how it's done.