I have a N/A 13B.....I have a RB exhaust with resonators, and a performance intake...aluminum piping and open element..

Would an HKS SAFC benefit me any as far as a lil more power?

 

Would better fuel mileage benefit you? Rotarys are set up to run a rich to add extra unburnt fuel to the cats to increase the internal temps and clean up the pollutants. Since you don't have cats, you can run your NA leaner which will not only improve mileage, but by running the AFRs closer to stoich, hp should show some small gains too. As to how much of a gain, ask your question in the 2nd gen section.