Many people mistake aftermarket intakes as the airbox only. For the record, the stock airbox is very efficient and most likely likely cannot be improved upon, including materials. However, there are other components of the system that can:
- Filter media
- Filter Mounting Flange
- Intake Charge Pipe
For example, here's a comparison of the intake charge pipe (left) vs Macht Schnell (right). The OEM filter mounting flange (not pictured) also has this restriction, a replacement is provided with the MS intake:
The MS piece also does not have the "accordion" type bend as seen on the stock charge pipe. A less restrictive flange, larger charge pipe
and high-flow filter (along with ICS scoops) all work together as a
package, resulting in best hp gains - which is why the entire system is included as a kit.
Hope this helps.