12a or a 13b???this is the question
 

im lookin to build a rotary for a project that im gonna do but am undecided if i should use a 12a or a 13b??
as of now i doubt ima turbo it, im probly gonna port it though like maybe a bridge port?

basicly what im lookin for is which would be better to use??

I would go 13b. Mazda stopped making 12a housings last year. You will get more hp and torque out of the 13b.

ok thanks for the info, i didnt know they stoped making the 12a housing.
now i just gotta find a motor harnes ecu trans and cross member.
lol shouldnt be to bad to find
anyone doin a v8 swap and got a extra 13b? lol

they stopped making earlier 12a housings they still have the later 12a housings.

hm, after checking i could be mistaken?

it dont matter i was already leanin towards the 13b anways, less hassle adjustign the carbs, easier starting, id hate to take it to a show and the dern thing not want to start b/c the carbs want to be pissy

The engine size will not matter as far as starting is concerned, it would all be dependent upon what carb you use and how it is tuned. You should be much more specific as to what project you planning on doing, as well. If you go the route of 13B, the port work you end up doing will be counterbalanced by it being a six port rather than a four port, assuming you are starting with a NA motor. If you do get your hands on four port irons for a 13B, then you'd be better off going the route of 13B, however, that would require you either finding ancient 13B irons or going with a turbo motor to start off with, and for the price of a turbo motor, why wouldn't you just keep it turbo as you'll end up wishing for the higher compression rotors if you make a turbo motor NA.

And once again, you need to be much more specific as to what your project will be so we can adequately give you direction.

itll be goin into a mini truck
so it seems like im gonna endup with a 6port?? the 4 ports are that hard to find?
and turbo woudl be nice but realy dont want all that clutering up the engine bay

also a 6port would be easer to mount because the mounts are on the sides of the motor right??? as the 4 port motor has a mount at the front of the engine???

The four port isn't at all hard to come by. The thing is that they have lower compression rotors which in turn means that you'll create less NA power, and you'll end up wanting to swap it out for the higher compression rotors.

Just do a 13B. For what it is worth, rotaries make little torque in comparison to piston engines, so hopefully you aren't planning to haul or tow anything, and you are just going to use this truck as a show truck.

a "newer" 4-port 13B is not that hard to come by, but yes, they are all turbocharged, so you'll have to get some high compression rotors and perhaps port accordingly. since you're doing a swap into a truck you may even want to put the Renesis on the table. if you plan to use this truck as a truck, then you should look up some of the threads that Jeff20B has started. he has a rather unique, disciplined train of thought when it comes to building rotaries, but i respect it. he's fathered some pretty good threads.

12A is a very durable engine, i would say start with that.

I'm much more fond of the 12A myself since it is already a four port and already also NA. Having said that, knowing what my plans are for my FB (which will be turbocharged), I'm going to be using a 13B.

It all boils down to what your exact goal is for your build. If you get a four port 13B, buy the higher compression rotors, and bridgeport it in comparison to how big the same port sizing would be in the 12A you'd obviously have more power and torque, but it would also require even more money considering the rotors would be separate.

Since the Rotary Pickups, REPUs, all came with the 13B, that's where I would start. Depending on how you want to configure the engine, carb/FI, you have lots of choices. You could try and locate a 74-78 13B, not easy, use any 6-port NA engine, all of which are FI, most can be converted to carb, use 85/85 13B housings with 12A irons and build a 4-port, find a TII block and build it with NA internals, etc., etc., etc..

Here's a link to the REPU forum, might give you an idea on how to proceed.

http://www.mazdarepu.com

thanks for the link, ive already looked at it several times, id rather haeea repu but find one! lol that5 will trade for a 91 s-10

anyways i guess im gonna go with the 13b id like to put some clatter carbs (i think), and id like todo either a half bridge or a full bridge port.