[Burger Steak & Eggs]

The HC filter is in the top half of the airbox. When the airbox is put together, the HC filter would sit just above the main filter. The HC filter is the same length and width as the main filter, but only about 1/4" thick. The HC filter media is flat and unpleated. "Filter" might not even be a good word for it, as apparently it is designed to block emissions from leaving the engine to the atmosphere when the engine is off. My reference is a VVTi engine, so your comments about potential different responses to mods is valid.