Field of application: 4" Supertrapp External Megaphone or Race Systems
Closed End Cap: Direct Replacement used on 4" Supertrapp External Megaphone or Race Systems.
Open End Cap: Will flow the equivalent of 10 discs w/closed end cap but give a bit more sound. If you are running 20 discs with closed cap you could go to 10 discs with open end cap and achieve the same flow rate. Also helps in reducing weight hanging off the end of the exhaust. Only for Off-Road-Use or Race Tracks!