I had an idea the other day. The RX8 computer keeps the engine
at stoichiometric mixture ratio at all times according to the OBD II data
I have captured so far on my RX8. Even under full throttle. Stoichiometric
is 14.7:1 to one as I recall so that is not the best for best power.
Best power happens at 12.5:1. Cheap way around this is to
fool the stock computer into thinking it is getting more air than it really is.
Consequently it will put out more fuel richening the mixture.

The idea is you program a $50 PICAXE computer to take data in from the mass airflow
sensor and the throttle position sensor and modify the mass air flow data going
to the stock computer when the throttle is wide open. This device
could be installed by disconnecting the mass air flow sensor and the
throttle position sensor and plugging them into the PICAXE. Two cables
coming out of the PICAXE could then be plugged back into the sensors. This way
the standard RX8 engine configuration can be easily and quickly restored by doing the
install in reverse.

On the other hand when the throttle is partially open during highway cruise
you could lean the mixture to get better MPG. The rotary will run at mixture ratios
of up to 17:1 or higher at steady speed low load  freeway travel.  I don't know exactly
what this will do to the catalysts so do this at your own risk.