[yelsew]

So it can route back into the exhaust and most systems will do this. You can also, if you like ridiculously loud "screamer pipes", leave it as is. Normally best for that pipe to be routed outside of the engine bay in a way it won't vent to the cabin, for whichever route you choose to take. Its some peoples style, but I personally recommend against it for the reasons of sound and gasses in the engine bay and cabin.