i'm re-registering my uk spec '04 rx in ireland for the first time and there is agrey area concerning the engine size,i understand that it's 1308cc but am told it is rated at 2616cc why is this and is there a way of confirming that the capacity is actually 1308cc?

 

Welcome to the club...

YES, technically it is only 1308cc, and yes many government registration authorities use the double up calculation to 2.6 litre.

WHY, well partly they do not believe the HP/KW can come out of a 2 Rotor Engine, other historic reasons.

In my state for Rego, they call the Mazda RX-8 a Sedan, not a Coupe, which is cheaper rego cost wise.
BUT, they also list the MX-5/Miata as a Sedan!!??, when it is a 2 door Roadster Coupe...go figure.

 

Well technically a 2.6 litre V6 only pumps 1.3 litres in a single revolution of the eccentric shaft, 2.6 litres after two revolutions (once all 6 have had a firing sequence). The Rotary after two cycles also pumps 2.6 litres as two faces of both rotors would have had a firing sequence.

So if you look at it this way, they both (the 1.3L rotary and 2.6L V6) move the same volume.