The H.O head flows better, and the H.O also has a completly different computer system. There are also some differences in the Fuel rail, injectors, and I think Fuel pump. It is possible to convert a Renix over to a H.O head, but you would probably be wise to change a few other things over, like the injectors (higher flow to match the increase air intake flow) and I think you have to switch over to H.O temp sensor (the renix has it in the head and the HO has it on the thermostat housing). The swap is possible though