I have a 83 and a 87 rx7. My 87 motor is blown. Would i be able to swap my 83 motor to the 87?

 

Yes you can do that but it will be really slow compared to before the engine blew in the 2nd gen. Best bet is to rebuild 2nd gen engine.

 

Yes, I agree with IanS. Also consider that parts for your 12a are becoming harder to find. Find a donor motor that runs. Search the local forum/for sale forum and see if anyone has a 13b local to you for sale. I was looking on Craigs list the other day and found a complete drivetrain, long block complete for $300. Said the motor even ran when removed.

Edit: yes Crit makes a great point that I was thinking about but didn't post. You would need to be a pretty good wrench to pull it off. I have an SE that needs a new motor, that's quite a bit easier to pull off.

 

You also need to consider that the 12A intermediate iron doesn't have studs for engine mounts. The FB cars are front-mount only. You can swap an FB front cover onto a 2nd Gen engine and use it in a 1st Gen, but you can't put 2nd Gen mounts on a 1st Gen without considerable work.

 

And the fact that all 1st gen 12As are carbureted...You would be swapping in an engine that makes 100HP on a good day...

 

it's not worth it. just rebuild the Gen II motor and call it a day.