One of those crazy ideas sort of
 

So i blew the oil control rings or more in the front rotor of my 91 13b. Found a post on craigslist for a complete 87 rx7 with a 13b with rear rotor problems.

Could I in theory take the front rotor and such from the second engine and replace the rotor and such on my 13b? What other parts would be needed? I assume the soft seals you replace when you tear an engine down regardless but is there anything else?

well in short ....no.... the 87 motor has different compression rotors, the housings are different. if anything was out of spec say a rotor housing you could not just swap s4 for s5 rotors/housings and vice versa.

+ 1 bad Idea

S4 is 9.4 to 1 compression

S5 is 9.7 to 1 compression

And if I'm not mistaken the s5 rotors are half a pound lighter than s4 rotors.

dually noted. Thanks