David Vizard theory is people generally run too much duration so cam companies run a wider Lsa to compensate, so basically you figure out needed lsa with 128 - (cid/8/valve size x .91) and the overlap you require and the duration sorts itself out, the formula is for I think a 10.5:1 cr probably need to go around 1 degree tighter lsa for 8.5:1 cr I forget exactly.
