OliverB
XS400 Junkie
You're not supposed to use synthetic in rotary engines; it's definitely a good thing you don't put it in the rx-8
Actually, lots of the "Rotorheads" are now using synthetic in their RX8s. Early on it was a no-no. Mazda uses it in their race engines because of higher rpms and heat production but they do get torn down after each race.
U.S. spec is 5W20 but everywhere else in the world Mazda specifies 5W30 and that is what I have been using in a blend formulation.