This is a tuned standaed Banshee head for the cub. The head mod on the standard head increases the efficiency of your head and thus your engine. If you look at the bottom of the head, you'll see the squish band, an angled ring around the outside of the combustion chamber. The angle of the squish band, coupled with the cc volume and bowl dimensions, determine how the air/fuel charge is controlled as it enters and exits the engine. Specific squish band angle dimensions on a given cc volume are carefully matched to the port design. With your head modified and the cylinder porting matched together, engineers have created a combustion environment that produces yet even more power.