Modifying the Factory Airbox

Paul took Dremel tool with a cutoff wheel and modified his stock airbox.

The airbox consists of three pieces.  The front two house the BCM and is held together with two bolts on the top.  The third piece is held on by two metal clips and that is where the air filter is.  This is the middle piece.  It would be on the "dirty" side of the air filter.
Paul cut out the retangular area as shown.
There is a duct that leads from the front of the airbox and directs air through the BCM chamber toward the airfilter.  I didn't realize it, but it's snapped in.  You can remove it with a little work.
This is what it looks like after you remove the duct.  View is from behind the headlight.  NOTE: the silver thing is the BCM.
Here is an interior view of the modified airbox with the air filter removed.
This is the view of the installed air filter, looking into the box from the "dirty side."

How did it turn out?  This is what Paul had to say, "Seems to pull better on the highway when passing.  It sounds GREAT!  The intake system resonates very loudly at WOT (wide open throttle a.k.a.: stomp on the gas) now.  I'm sure it sounds very distinct coming down the street.  Sounds as docile as ever at normal throttle positions.

  Paul removed the front section of the airbox that once held the duct.  These are photos of the airbox with the driver's headlight removed.  The left photo is the airbox with just the duct removed and the right photo is with the front of the airbox removed.  Paul reports there does not seem to be any improvement and the intake becomes even louder.  So if the noise bothers you, he wouldn't recommend removing the front.

Randy did a similar modification to his Impala.  He says that along with the increased response, his gas mileage went up, from 26 MPG on the highway to 32 MPG from his latest trip.

James, another Impala owner, performed a similar modification.  He removed about 3/4" off of the air intake duct where it meets the filter media.  He also saw performance gains but shortly after his engine began to bog and would hesitate, most notably going uphill.  He has had the PCM re-programed twice but it hasn't fixed the problem.  James says it might not have anything to do with the mod, but it was the only thing he changed before the problem occurred.