Rotory engine efficiency

Why do rotory engines generally have poor mpg and high emissions, also why are they said to have poor heat efficiency? The Mazda RX-8 Renesis engine claims to minimize many of these inefficiencies, how true is that?

Rotaries, by design, are inefficient because of the long combustion chamber (high surface area to volume ratio, allowing more heat to escape into the coolant), and because of the relatively low compression ratio.

I don't know much about the rotary in RX8, though. I think it's just evolutionary stuff around the board, with side intake and exhaust ports, instead of side intake and peripheral exhaust (I think - might be the other way around).

Casull hit the nail on the head. If you look at a diagram of a rotary engine, the biggest and most significant advance of the Renesis (the new RX8 rotary) was the move of the intake/exhauts ports to the side/wall of the combustion chamber. Just look up the renesis and look at the difference. The change increases efficiency and cancels out alot of the fuel and heat ineffienciencys. Sorry for any incomprehensible type--I am drinking Jim Beam Black and coke at a friend's party. Later--

Jon

Just to clarify, we mean "side" as in the flat part, not the curved part of the chamber.