I think Static is right that the RX-7 almost always had 2. Unless you wanted a dragster with 4 rotors - http://www.youtube.c...tch?v=EebTCsiP3rs (0:37)

Or 6 - http://www.autoblog....-and-sounds-like/

But, no pistons.

It doesn't have any valves either. :-)

Cheers,
Scott.