well as you can see , theres not too much knowledge about cams for the rb25 s . like you said the limiting factor seems to be the hydraulic lifters . maybe you have to go to solid lifters , seems to be plenty cams available for the rb26 with big lifts and durations , and they,ve got solid lifters . i,ve got a spare rb25de head lying around so must check it it out and see what can be done .