A&Q about 350Z
Q:
just wondering somthing, i have used many carbed engines with the top off the air filter for a few minuites in a filtered shop and they ran fine, no backfiring etc that i have heard of, my question is, there are tubes cmoing out of the rocker cover that lead from that and attach to the top of the filter disc after the filter (in the centre of the disc) what is this for? is it for if the oil surges it just blows into this and gets burnt off instead of blowing the cover or spilling everywhere?
A:
They are for PCV. The PCV valve opens at part throttle keeping a flow of fresh air through the crankcase. It helps ring seal, pollution, and evaporating contaminants out of the oil. The air source for the crankcase comes from these tubes so they get filtered air. Some tubes go into the air cleaner assembly before the filter, but they typically have the little scotch-brite looking filters inside.
They often have black oily residue on them since the atomized oil works its way up that tube when the PCV is closed.