Hi, I’m new to the rotary world.
To make story short I bought a 1981 fb with a 13B
recently order some maintenance parts (oil pan gasket). When I removed the old gasket to my suprised the one that I ordered from racing beat was a tad smaller that the one removed. Another thing is the engine is a 4 port if that helps.

 

12a was original to the car. if that's the gasket given to u then yes it's shorter front to back.

 

I ordered the gasket for a 13b.

 

If the gasket they sent is about 3/4" (20mm) shorter then it's a 12a gasket. Call them and tell them there was a mistake.

 

I’ll give them a call tomorrow.

 

the rotor housings are 76-78 13B, with 81-85 irons, its basically an old school 13B, but with the better nitrided irons. If Mazda had a 4 port 13B in 79-80 it would have been like this.

 

It's the same type 13B I have on the stand now.... '84 12A irons mixed with '84 13B housings/rotors/front cover/E-shaft. A '70's style 4-port 13B made from '80's parts.

 

Also, you don't technically need the oil pan gasket. You can just use gasket maker/RTV. I used black RTV, and it's held up well.

 

the factory uses silicon, Mazda number is 0000-77-1217-ES, $11 list price. its a Three Bond TB1217D. the permatex right stuff, is good too