I'm getting ready to do an engine swap in my 90 RX7. I got a wrecked 86 w/ a good engine & low miles.
What problems I’m I going to run into with the 86 engine going into the 90?

 

I did this a long time ago. There are a couple of things you have to do.

1. You will have to use the font cover from the 90 because of the OMP.

2. Of course, you would want to use the 90 intake.

3. You will need to make a blocking plate for the EGR valve.

4. There is a freeze plug on the intermediate housing below the primary intake ports. You need to check for clearance. Use a straight edge to make sure that the round part of the freeze plug doesn’t stick out to far. If the FP sticks out to far you will need to tap it (dent it) so that the 90 intake will not touch it. If you don’t do this, it will be a vacuum leak that you will never figure out and your car will not idle!

5. You might want to stick with the 86 Crank Angle Sensor, but I don’t think it matters. I used my 86 CAS

Everything else is a GO! Oh one more thing remember the 86 Red lines at 7,000 not 8,000 but it didn’t seem to hurt mine. hehehee

 

http://www.rotaryresurrection.com/series4swap.html

 

Thanks for the tips.
I'm going to take my time and do it right. The car isn't my daily drive so I don't have to rush. But i can't wait to get it done!!!! :-)