I know how it affects lift but how does it affect duration? For example how would the duration change between a 1.6 to a 1.7 rocker? I don't think the actual numbers would change but wouldn't you have more lift sooner?

 

That is correct. That actual seat to seat duration does not change. So the idle quality and the vacuum remains the same. What does change is the valve will be higher in lift at a given dimension such as .050". So the effective duration will be higher once off the seat. I have seen numbers such as 2 degrees bandied about but I would think that would depend on the acceleration rate of the camshaft lobes.

 

It seems like you could see big gains on a stock cam with forced induction.