if you are chasing power go with 1 piece titanium valves , there is a aftermarket company that does them , most oem ti valves are 2 piece that are welded together and they can break as i recall , yamaha yz250f 06 model had a recall on these and replaced them as they were breaking near the weld , the 1 piece valves solves that problem , another thing is to get is some decent valve guides fitted as the oem guides are average , this will make the head last longer and the head is very important on these 4 bangers especially if you are chasing power.