quoted for the haters :
another take :

actually this is correct. each face of the rotor has 654cc and there are 2 rotors, so thats 1.3liters. every time the rotors go all the way around, the drive shaft goes around 3 times, thus every revolution of the crankshaft has 1.3 liters of displacement fired. However in piston engines, it takes 2 rotations of the crankshaft for all the displacement to fire, thus you take the displacement of two revolutions of the driveshaft in the rotary, which is 2.6liters.