From what I understand it's for the cylinder deactivation feature. Basically to help with sound when the v8 turns into a v something else lol. With aftermarket exhaust it doesn't help much and the muffler shop said they get people in their shop all the time with couple year old vehicles complaining about exhaust rattles or sqeaks. 9 out of 10 times it's the flapper after it gets dirty and corroded. Basically it causes more trouble then it's worth. Kind of like DFM 😅Stupid question, what is the flapper? what is its purpose?