12A and 13B interchangeability?
 

I'm figuring out how I want to piece together a street application NA 13B engine. What (if anything) is interchangeable betwen the 12A and 13B motors?

I figured 13B is the way to go for it's displacement as we all know how the saying goes. But I'm curious if there are any advantages to possibly using any 12A parts?

Are irons (is that what they're called?) and housings at all interchangeable? Rotors? Eccentric shafts?

Any weight advantages to be had either rotating assembly or even just the exterior irons/housings? Maybe little-er parts accessory parts like the oil pump and water pump? Oil injection system?

Reducing the overall weight of my long block (if possible) is a priority for me.

What about intake and exhaust manifold patterns?

Or should I only be looking at 13B stuff...?

Please forgive my ignorance, I am new (sort of) to rotaries.

appreciate any input,
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13Bs and 12As used the same parts when they were both concurrently made, aside from length. A '74-78 13B was a longer '74-78 12A, a GSL-SE engine was a longer 6-port 12A with fuel injection. (I do not know what 6 port 12As came in other than that they were carbureted) Anything not related to length was the same.

There is no functional advantage to using 12A parts aside from possibly availability, if you were keen on building a 4 port 13B. (Which in this context means a '74-78 13B. Turbo II and FD engines are four port engines but are generally not called "4 port 13Bs", they are just Turbo II or FD)

After 1986, Mazda made significant changes to enough things that you can't use 12A parts in anything except for some bolts and stuff. Almost all of these changes were for the better, and the parts are more available, so the best bet in 2023 is to just buy an FD longblock. Even with the 9:1 compression rotors it will be just fine naturally aspirated.

For 13Bs there are three different intake BOLT patterns but this does not mean the ports will line up. There's 4 port, 6-port/Turbo II, and FD. I forget where 13B-RE engines fit into this, I think they are the same as FD since they were also twin turbo engines. And just because something bolts on does not mean it works well...

Appreciate the input, I have read up a lot on the topic since and I realize my question is a bit too vague and there is no simple answer to it.

Looks like once I figure out which irons and intake manifold I want to run that should narrow things down for me regarding the 4 port/6port and 12A/13B options and I'll have to re-visit the drawing board again then.

what car is it going into? the easy button is just to start with something that will bolt in.

for example an FC. the FD engine is cheaper than the T2 engine, but you need to buy $350 worth of mounts to get the FD engine in the car, which makes the FD more expensive...

From all I've read a four port motor makes better power when street ported than a 6-port. At this point in time either a TII or an FD engine would probably be the way to go. Like j9fd3s said may depend on the car it's going in due to mounting options.

If I understand correctly the 13B-RE Lower intake bolts on to the 13B-REW and vice versa, but needs some port matching. There were some FD guys running RE mainfolds on their REW engines.