It ran a 3-rotor with 8.5:1 rotors and was turbocharged producing 320hp @ 7000rpm and 290ftlbs. "...ceramics are used for the trochoid chamber's sliding surfaces. A trochoid shaped ceramic core is pressure-fitted into a heat expanded aluminum housing." The rotors were made of aluminum and the apex and side seals were ceramic. Other seals had higher heat resistance due to the thermal insulating characteristics of cermamics.
Apparently "The new ceramic material could readily be used for other important components in the rotary engine; for example, the side housings (cast iron in the MX-03 engine) and side seals. Such componenets are being developed at Mazda, although the MX-03 does not include them."
"One remarkable feature of the ceramics is that they can be machined: port openings, sparkplug holes and seal grooves are machined into the inner core and housings. The exhaust port is also fitted with a heat-retaining ceramic insert-a natural application ofr the material."
Yamaguchi, J. K. RX-7: The New Mazda RX-7 and Mazda Rotary Sports Cars. Pg. 216. St. Martin's Press. New York. 1985.
My take:
Imagine how light the rotary would be if its make up was entirely ceramic! I imagine the costs of doing this would be prohibitive. A set of ceramic apex seals from Mazdamotorsports will set you back around $2000 US, as opposed to steel seals at $300 US. Granted there is no mass production economies of scale in place, but aftermarket companies such as Atkins, Rotary Aviation and Hurley are able to produce steel apex seals for a similar retail cost as Mazda and they are hardly large businesses.
I believe that a more desirable development would be towards aluminum rotors and intermediate housings. Given the widespread availability of all aluminum four and six cylinder piston engines, the rotary's weight advantage over the piston engine is not nearly as significant as it was. In order to justify the rotary engine's continued production, improvements must be made.