I installed a K&N drop in in my K20Z3 without tuning and all I got was a more intimidating throaty growl but lost more precious torque. It seems the stock airbox design will suffice with just a K&N drop in even with more aggressive camshafts installed. I settled with the stock filter until I get my cams from Santa.

Check out Ex Manila for complete exhaust systems. I heard they supply Orange Performance.