Ports have been reworked on inlet and outlet to get a better flow, and they are bigger on the outlet. Never looked onto the inlet of my RSi head. It came with a hotter cam (272°), solid lifters but standard valve springs. Inlet valves have been reworked to get a better flow. And the head has been skimmed so the RSi has a compression of 9,9:1, while the XR3 with the same bottom end has only got 9,5:1