Here's what we think

RX8 is gone

Too bad that the rx8 is gone. It burned its oil, had relatively poor fuel economy for the power output, and was generally lacking in torque (twisting force) relative to the high-rev peak power. So the renesis was flawed, but it was so simple. The worst aspect of owning an rx8 was that the three (!) moving parts generally stop their miraculous dance every 60-80k miles when a rotor tip seal finally wears away enough that the engine can no longer maintain compression. The fix for this reliably-predicted failure mode is to remove the tiny engine, disassemble it, and rufurbish the rotors with new tip seals. Without other parts that might fail unpredictably and without certainty as to which has gone wrong, the rotary is therefore only a single flaw-acceptance by the public from being able to be thought of as a “forever” engine. I imagine that once such a widespread acceptance of the expectation of a regular rebuild was achieved, the cost of rebuilds could have been built into the purchase price and even reduced in cost by a factory-run exchange program. The expired engines could have been rapidly exchanged, for a marginal-cost-of-rebuild fee, for a dealer-inventoried ready-to-go entirely fresh engine. The rx8 could have even been designed/redesigned to facilitate the time to complete a swap. I have to admit the appeal, in the context of planning a boxster-based kit car, (particularly around a low-output ’97-’98), to plan to replace the weighty and wide boxer with a rotary when the german engine fails. The similarly powerful rotary weighs 200 lbs less, has a similar center of gravity height, is shorter (lengthwise), easier to service, facilitates a smaller moment of inertia, and would particularly aid decreasing suspension forces in response to roll-movements.

I thought the rotary would really work well as part of a hybrid-electric drivetrain. The design’s tiny weight per unit power (and per unit torque, actually) would allow a very small rotary-engine-generator, and the saved weight would significantly offset the weight of a battery pack and power electronics. Also, the small rotating mass of a rotary and its high rev limit (can’t valve-float a motor without valves) would better run parallel with the speed and mass characteristics of an AC induction motor. However, each force-generating component somewhat covers the other’s failings. An electric motor has maximum torque at a dead stop and a rotary’s builds and then plateaus at a speed that electric motor’s would decline. Also, the handoff-overlapping operation circumstances of each motor would allow a rotary to fend off its rebuild-hastening weaknesses: excess heat and running hard cold and being shut off rapidly. With an electric motor and its likely electrically-operated coolant and lubrication systems, the rotary could be eased awake and back to sleep without having to provide the resources to manage those burdens. Also, iirc, a rotary could run much higher compression ratios and generate less lubrication-gobbling heat if it were designed for a narrower range of operating speeds (mostly higher at the lower range) and for more intermittent periods of whole-vehicle load. toyota should license it from mazda for a sport version of the next prius or something.

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