what is the purpose of this plenum or whatever it is called hanging off the bottom ? This is the duct that runs from the air filter box to the throttle body on an 8.1L in a 2006 Sierra. I mistakenly got a duct for the 6.0L gas engine which is slightly different shape but that also has a plenum thingy hanging off it.
I am going back to oem configuration on the truck. It came with a K&N cold air kit- cone filter replaced the air box and the K&N duct was just a straight pipe that went from air box & MAF sensor to the throttle body.
So my question is how come the OEM setups have this plenum thingy, what is it's purpose? And why does the K&N setup not have it?
here is a pic of the k&n setup