I'd assume a high-comp engine needs a turbo specced to it, propably one with a nonrestricting exhaust housing, then proper active knock-detection or ion-sensing, and a huge cooler plus perhaps added water injection. I would think the mapping is also much more critical. It would be interesting to know in detail what kind of management setup the WRC cars are running. I think those cars run crazy high C/Rs to combat the restrictor.