RE: OS BGX in Dominator 1500 class
straight from the USRA Rule Book
3. ENGINES - SUPER TIGER 3250, or MOKI 2.1, in stock configuration with no modifications and equipped with a stock muffler that is cataloged for use on that engine. Tuned pipes are not allowed. The tank should be setup for muffler pressure, crankcase pressure and bladder type tanks are not allowed.