The gains with this unit are somewhere around 3 whp. Not enough to feel, but the car will breath a lot better. Also the ram air duct will see gains when you're over 60 mph, something a dyno cannot give you power numbers on.
Without a doubt this is one of the top 3 intakes available for the RX-8. The only drawback is that it's not going to be usable down the road if you get a supercharger or turbocharger. Not a flaw with the intake, this applies to virtually all aftermarket intakes for the RX-8
What do you think of installing performance radiator? Would a be a easy while also installing the RB intake? Do you still have the instructions of disassembly?