Tegheim - Home made 4 rotor Wolvo 142

[Libor]

Originally Posted by Pettersen

It refers to the shape of the combustion chamber.

LDR = Leading deep recess Good performance high emissions.
MDR = Middle deep recess Compromise to get down emissions.

Well, I have seen too much data on this stuff so I forget most, but looking at "Recent Technology Development of High-powered Rotary Engine in Mazda", its clear that MDR design produces highest BMEP from all tested variants, especially in the top-end. Note: this is with both spark plugs. Second best was "leading flat" recess and LDR design was third as far as power goes.

With leading only ignition, leading flat was best and LDR/MDR were about the same at the top-end, LDR slightly better in midrange, but both considerably worse than leading flat variant. But the point is moot since the most people do use both spark plugs.

IIRC R26B and 13G also has MDR rotor pockets. Maybe this desing has bad name due to Renesis rotors, but their problem probably lies much more in inferior gas sealing - low dynamic compression.