AEM has researched it, to come up with the perfect size intake tube. If you use a large pipe such as a 3" Akimoto intake, there is plenty of space for air to travel from the filter to the TB. Then if the pipe dia. is reduced then the speed of the air needs to increase to supply the same amount of air. Now if the pipe dia. is too small, then it becomes restrictive. And AEM as found the perfect balance between the too. Plus they use K&N filters. Can't beat that.