There are a laundry list of changes to the S2 that make it better than the S1. A rebuild of an S1 doesn't really make it equal to an S2, it's just a reset button, but you still have the same S1 issues that will cause problems eventually.
https://www.rx8club.com/series-ii-technical-trouble-shooting-160/mechanical-changes-rx-8-series-i-ii-161665/
The key items that point to longevity for the S2 over the S1 are the upgraded oiling items. They changed how the oil metering works and added another oiling port in each rotor housing so you have a total of 6 in the S2 motor vs 4 in the S1 motor. Those things really can't be added to the S1. You can get an S2 starter and put it on your S1, and that is advisable, especially for the really early cars which had weak starters, you can also put better coils on it, but you can't redo the oiling system on the car.
If you did a rebuild so that the engine was fresh and then pre-mixed I think that would be somewhat equivalent to the S2 setup, but I'm not certain.
You can't put the S2's MOP system on an S1 (or could you? It's just the rotor housings, lines, and MOP itself right?) but you can premix on any of them. And knowing now what I've found with experimentation, Mazda really under-oils everything that was ever made with a catalyst. So anything made 1981 and newer.
oldrotarydriver wrote:
Freshening ("preventative rebuild") could probably catch something about to fail, not necessarily in the combustion chambers. Water jacket seals had a bit of notoriety for failure in the earlier engines / rebuilds, as an example.
I note with pleasure that Mazda moved the coolant seals back to the rotor housings on the RX-8 engine. The '86-02 engines were prone not to the seal itself failing, but the lands in the side housings that support the seals would break out, and then the seal could walk out of position.
The biggest problem I've run into with pulling an engine apart for refresh is finding that the apex seal slots in the rotors are worn out. Now you need to replace the rotors, which isn't always possible. (Anybody with '83-85 12A rotors in good shape is sitting on a gold mine!) That measurement is absolutely critical, can not be higher than .0025". More than that and gas pressure behind the seal is lost too quickly, and the seals can bounce and chatter, which is bad not just for performance but also seal and rotor housing life.
