seems like they are they same IM for the most part except the runners are larger on the RRC. It may work better on my PRB-1 head with DIC. I want to open up the RRC and port it like the RBC I did.I think that is the key point. It is responsible for this massive torque peak at around 6000 rpm you see on most RRC dynos. Past 7000-7200 power hardly climbs anymore.
My CNC ported RRC had the same characteristic. I did not like it for this reason in my Elise.