P1SC question
You would always what to have a negatine pressure in your crank case. This would help your rings to seal against your cylinder walls. "MAKING MORE POWER"
I believe that tube is called the fresh air inlet for the pcv system. In a stock setup metered air is pulled in there, goes through the crankcase, and exits the back tubes which come around to the pcv valve and then goes in the intake manifold. ATI moves that line to a pre-blower location so you aren't blowing boost through the engine. The downside is that doing this causes unmetered air to enter the intake via the pcv valve at vacuum conditions (i.e. part throttle), and most of the time ltrims rise and you have a general lean condition. Some people have moved the maf in front of that tube so the air gets metered. Some good results, some bad, it didn't work for me. Well it did 'work', but had other problems arise. Currently I have no pcv system. Experimenting with it and breathers.
<small>[ March 30, 2003, 10:47 AM: Message edited by: AzzHauler ]</small>

