Adding the larger ratio essentially adds cam lobe to the cam. In other words....when the stock cam cracked open the valve,(just off the valve seat) swapping to the larger ratio is now putting that valve hypothetically .030". The same for shutting.....the larger ratio is extending the valve open timing. This is great for the intake valve but real bad for exhaust.(not really but killing a tad bit of power) And retard the cam puts the intake valve opening at a stock location and will be extended for shutting. Using the stock exhaust rocker along with retard cam will put the exhaust opening shutting points in a great location as well.