OK i was just talking to a friend about going through with the 13:5.1 on my 03 yz450. I told him i figure by doing this it will be better for piston to valve clearance since i am running stage 1 hotcams. He seems to think, that by doing so there will be to much compression and i have a good chance of damaging the valves if i dont get stronger ones such as titanium or such. Mind you this is coming from a car mechanics standpoint, but i figured i would ask the masters. I am looking for that beastly low and mid without a bore so i figured this would be the way to go. But is it nescessary to do the valves and put ones with more guts in?