ok, i thought about it b4 and now im bored so i will ask this... if a 20b is simple a 3-rotor powered motor, and a 13b is 2 rotor... cant you just add on another housing and a rotor to a 13b to make a 20b? or is a 20b just actually the rod and rotors that are on it. and those who know a grip about this or the rotory engine in general, if youre plannin on callin me newb or something then i say this to you... we all have to learn somewhere. thanks guys, and any extra info on 20Bs would be awesome. thx. l8.

 

Go ask in the 20B forum, you get the best answer there.

https://www.rx7club.com/forum/forumdisplay.php?f=95

There is a FAQ in the forum about the 20B there to.

 

Basically, you need a modified eccentric shaft. For one, you need rotors that are 120 degrees out of phase vs. the 180 you have on a 2-rotor. Also, you find that you can't just slip a 3-rotor together - you actually have to use a 2-piece e-shaft that's joined inside an intermediate plate, so that plate will be thicker than the other. There's plenty of other little oddities, but those are the major obstacles.