Originally Posted by wstar

They are, in fact, PCV-related. The PCV system has two lines (per side of the engine in our case). There's a vacuum line that goes from the intake manifold to the crankcase, which puts negative pressure on the crankcase and sucks out crankcase fumes via engine vacuum. That's the one you typically put a catch can on to get most of the nasty stuff. Then there's another line which is fresh air delivery to replace what that line sucks out. It's the fatter, baffled stock hose that attaches to the side of the main air intake tube and has a baffle in it.