has anyone installed one of these? whatre they supposed to do exactly?

 

Do you mean an air filter?

If you do, it filters the air thats coming through your air intake and removes anything that could f**k with your engine. Mainly, when you have clean air coming in, it feels better.

 

i think what he might be talking about is the small sized filter that goes on the valve cover.

 

If you're talking about the breather filter that goes into the valve cover it vents pressure from the crank case. The PCV does the same thing in the more environmentally friendly way of recirculating the gasses back into the intake to be burned off.

High performance engines use breather filters because at high RPMs oil particles can get sucked up into the intake. This can cause some issues for a race engine.

 

actually, it can cause issues for any car depending on how you drive it, if you ever take your car to an autocross event, you'll see it in action. under hard cornering, some oil can be picked up by the PCV valve and then it(the oil) continues into your intake manifold and on into your cylinder, and oil in the combustion process can lead to detonation. the downside is however, the pressure being vented from the crankcase is from some blow by past the rings into the crankcase, and is usually higher in NOx than the exhaust gases because of the location it came from in the cylinder, and it would be vented directly to atmosphere.
Just like any modification, you have ups and downs.