Wankel as an engine design is interesting if you only look at the headline figures such as power output vs "capacity" or power output vs size.
They are generally smaller than an equivalent power output piston engine but are also much less reliable and have a limited running life if abused.
So, if you need a lightweight, powerful, small engine, but are happy to do engine rebuilds every 40-50k miles, then a Wankel is good.
In practical terms they never really took off due to the maintenance costs and poor fuel economy.
I've ridden 2 Wankel bikes, a Van Veen OCR and a Norton Commander and whilst the power was good, it wasn't that good, and the complete lack of any engine braking whatsoever is seriously unnerving. I'd love to try a more modern Wankel but hardly anyone is developing them, especially now that electric cars are destroying them in power output vs size/weight terms (not including batteries or fuel tanks).
You can get 220bhp out of a 690cc piston engine if you turbo charge it and let it rev to 20,000rpm (pneumatic valves?) but that won't be very reliable either. :-)
A friend has an RX-7 Twin Turbo and it's a rocket ship of a car but that's because is puts out 240bhp in a 2900lb car.
It averages 22MpgUS and has so far needed 2 rebuilds for new rotor tips. It has done 82k miles.
