Right now I have a Kart with a rotary engine in it. It's great fun, but it lacks power coming out of the slow turns. Is it possible to somehow put in a 2-speed gearbox? First gear should be a lower gear so I have more revs at low speeds and 2nd gear should be what I have right now. Maybe you can put something in between the 2 sprockets or some kind of planitary gear onto the rear axle?

I'm sure someone will be along shortly with a more complete answer. But you may have some luck looking a autograss supplies/cars for ideas as i know that most of the top class's run fairly simple 2 speed boxes. Don't know exactly how they work but it might be a good place to start.

Imageshack is down so I can't put pics up. On these sites you can get a good example of howmuch space there is and how the chain connects the 2 sprockets.
http://www.kart-racing-baden.de/html/wankelkart.html
http://www.p1kartcircuit.com/home/index.php?option=com_content&task=view&id=19&Itemid=42