[blykins]

Originally Posted by olddog

Well yes and no. The Chevy sbc guys have changed out their 1.5 ratio rockers for 1.6 ratio rocker for 50 years, or more, to get a bit more performance. It increases lift, but it also increases the 0.050" duration a tad bit, too. We all compare the 0.050" duration because it is generally accepted that nothing significant is happening below that. I read where they have actually measured the 0.050" duration before and after a rocker ratio change, but I cannot recall the actual numbers. It seems like it was a degree or two on each end for a total of 2 to 4 degrees duration change. It can be around 25 hp on a dyno. Nothing huge, more like a little, but never the less some change.

Now if you were to tell me that it is so minimal an impact on idle quality and low end manors that it is not worth the work to change out the rockers (let alone the cost), I'm totally with you. However changing out the rockers is a lot easier to do than changing a cam, with the engine in the car. So then the question would be, is a few degrees less duration going to make much of a change in manors? Theoretically going in the right direction, but is it insignificant?

Changing to a higher rocker ratio will affect duration, but it does it by a rather insignificant amount, like 1-2°. A 1-2° change at .050" duration isn't going to be enough to change the engine's manners or driving characteristics, or in this case, change the engine's personality into something docile.