As far as ex. port (timing) is concerned , it is linear movement in reference to movement per degree of rotation. In this area of the stroke, that rate is fairly constant. BUT, since you have increased the stroke, movement is more with the same given degrees of crank rotation. Thus, your exhaust ports open 5 degrees earlier. And since they open up 5 degrees earlier, they close 5 degrees later ,bringing up the (duration) to 10 degrees more than stock....Jim