Never run a 2.6" pulley with the stock injectors ... 2.6" pulley at sea level boost as high as 22.1 PSI logged with the Aeroforce Interceptor Gauge.

 

I installed a K&N high flow filter with the stock airbox with no lower cover. BUT it's held in place with the screwed clamp that comes with the filter. You just have to make a small hole in the side of the box to be able to get the screw tightened. It's not half assed.