'86 chassis IIRC is the lightest. S5 rotors and intake superior to S4, those are the two biggies for hp. Lots of other differences between the two, with "better" falling in both buckets.
I ran a S4 shell, S4 ECU w/ clipped limiter, S4 housings, S5 rotors, S5 intake, S4 TB and AFM and the car made power.
Take a look around at rx7club.com and you will find lots of information on the various differences. The best car is half S4, half S5.
Mark B. - Dallas, TX
#76 RX-7 2nd Gen
SCCA EP
Former ITS, ITE, NASA PT
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