it's actually been a common misconception a few people have tried to convince me that the rx8 comes wih the option of a 3-rotor. First, a 3 rotor 13b wouldnt make sense, the 13 represents the 13 centiliters of displacement, mazda would have had to have made the housings considerably smaller, that will probably never happen. All currently available rx8s come with a 2 rotor RENISIS engine that has been assigned the code 13b-msp.

 

Mazda actually made a 13G that was a 3rotor "race" motor made from 13B housings, it is call'd a 20B short block