Is it possible to change out a 1991 13b motor for let's say a 1974 12a motor? What kinds of changes would need to be made?

 

Need more info..what is going into WHAT?..
13B in an FB or a 12A into an S5?

 

I have a 1991 rx7 (13b) the motor is in peices and needs to be rebuilt and I have a new 12a motor can't I swap them out or will the 12a intermediate housing work in the 13b motor?

 

welcome.

of course it can be done. I've heard of a few cases scattered here and there, may have even seen a photo of a 12A in a Gen II. never seen one in real life though.

things to consider ...
mounting
low pressure fuel system
wiring the ignition
oil pan clearance

a true 12A intermediate does not have the provisions for mounting. not to mention, you'd have to deal with the mismatch at the coolant seals.

my opinion: a 12A conversion is not worth it! inventory your 13B parts and have it rebuilt if possible. if not, look into other viable 13B options.

 

I knew they were that different but i wasn't sure by how much thank you for the advice.

 

Im going to try and rebuild it if i find the money and all that thanks for the help