12a 13b 20b are they related
 

i have well i am going to be getting a 12a this saturday, and i wanted to know if the rotors are same size on the 20b engine or any other engine for that matter..... and is there a way to convert to a 3 or 4 rotor engine like a longer rod or something, cause couldnt you just stack another rotor housing in with the others? please responde but be gental im new at the rotary thing. ;)

IN the beginning, there was the 10A. Two distributors (one for leading one for trailing), 5mm carbon-aluminum apex seals, two sets of side seals. It had 60mm wide rotors.

The 10A begat the 12A. It was identical in construction and dimension, except the rotors were 10mm wider - now they were 70mm wide.

There was also a 13A, but it wasn't related to the 10A or the 12A, so we will ignore it for now. But it is important to know that it did exist.

In 1974 there was great change. The apex seals became two piece 3mm thick iron seals that had a much better lifespan. The distributors were siamesed into one unit. The dual side seals were replaced with single units. And the engine dimensions changed. The 10A was no more, the 12A was retained, and there was a new engine created by making the rotors 10mm wider again. This engine (with its 80mm wide rotors) was known as the 13B. Why 13B? Because 13A had been taken already.

In 1986, there was more great change. The 12A was dropped, leaving only the 13B. The 13B, still with its 80mm wide rotors, received thinner side seals, 3-piece 2mm apex seals, and the coolant seals were moved from the rotor housings to the side housings, where it made life hell for people. The 13B remained like this until the last of the FD's in 2002.

The 20B is, in a nutshell, a 13B times 1.5, with the necessary adaptations for efficient cooling and ease of assembly.

All of these engines - 10A, 12A twin-dizzy, 12A single-dizzy, 13B 3mm seal, 13B 2mm seal, 20B, even the new side port 13B, have the same trochoid dimensions... the "radius" and "stroke" if you will. All displacement changes were made by making the rotors wider, or in the 20B's case by adding rotors.

"Stacking rotors" is a dream of many but in reality it takes a lot of work, and you end up with a heavy, expensive, long mess of an engine and 9 times out of 10 you're better off with a V8 in the first place.

The 13A, which we will go into now, was a rare engine. It was the only *production* Mazda rotary that did *not* have the same trochoid dimensions as the 10A/12A/13B/20B. It had 60mm wide rotors but a longer "stroke". This was to keep the engine as short as possible, since it was mounted in a front wheel drive car, the R130 Luce ('69-72).

thanks for the great info

good writeup on the different engines...thanks for the knowledge!