ok well i have A 1990 13B INJECTION FC. i heard that with the non turbo motor you can just have a straight pipe for an exhaust and make more power then for say buying a racing beat exhaust or something like that..can some body help me out with this. im new to rotorys if thats not noticeable lol

 

im no expert, but what i know is the s4(86-88) has 5th and 6th intake ports that open with exhaust backpressure, so the exhaust cant be that "free flowing" for them to work.
on the s5(89-91)the 5th and 6th port open with pressure from the air pump, so you can almost have any exhaust on.

 

Rotaries respond well to exhaust modifications, but keep in mind that an uncorked rotary will deafen everyone within a 5 miles radius. A high quality full exhaust system like what RB sells will be streetable, yet only cost a small amount of power over a fully open setup.

 

I have racing beat exhaust on one car, and muffler shop straight pipe on the other... the straight pipe is probably twice as loud as the racing beat exhaust on the other car. However, racing beat stuff is expensive. Your call.