Okay pretty simple, there are different rotary engines in the Mazda line up. Most common will be your 12A, 13B, 13BT, 13B-RE, 13B- REW & 20B. All of these I just listed are all 2 rotor motors except the 20B which is a 3 rotor. There are others, but to keep things simple that's what will most likely hear about. The are FAQs that will help you out if you decide to read them. There are a few types of bridge porting (half bridge, full bridge & monster bridge ect.) It is called a Bridge port because in the process of getting more air into the engine a slit is cut into the plate parallel to the port & a bridge is left between them for the seal to ride along. Now Peripheral Ports are different completely as the stock ports are closed off & the intake ports are cut into the rotor housings themselves above the factory exhaust ports. There is a Semi-Peripheral port which the factory ports remain in the plates & small peripheral ports are cut into the housings. Manifolds will be interesting for these type motors. Read here for info on porting:
http://www.rx7forums.com/forum/showt...=7899#post7899