I believe it was an actual turbo (turbine powered by exhaust flow). From the noobs at Trx, it works somewhat, but leans out the motor quite a bit. For the cost/complexity, just get a bigger motor that has the power needed without tricks.
Edit: Oops, I guess I was mistaken; it appears it is a supercharger (belt driven):
http://www.rbinnovations.com/category_s/3.htm