There is more to consider when choosing a rocker arm than just ratio. Just because a rocker has a certain ratio doesn't mean it will work. The geometry and spacing of the trunion to the pushrod cup and roller tip are actually more critical. Thats why most engines have their own unique rocker arms that are made for their own specific valve spacing relative to the rocker stud or rockers shaft. A custom SBC rocker for instance, with a 1.7 ratio will not work on a BBC, even though the BBC uses a rocker ratio of 1.7.
