About a month ago I put an aluminized glasspak on my '99 Flareside 4.6 auto. I kept the stock tailpipe since it is 2.5". It sounded great, just what I was looking for and the price made the swap even better. I reset the computer after the muffler change and the truck ran better than stock but still felt a little lazy right after changing to 2nd and 3rd. Had been considering removing the silencer from the airbox but when I took it apart yesterday I can't see where that would do anything except open up for more air but would also slow the velocity entering the throttle body. Stock, it narrows as it approaches the throttle body so this should increase air velocity IMO. So I decided to do the airbox mod that ShaneM007 did on the V6 forum. I cut the part of the box that holds the filter. This exposed 1/2 of the filter and is now similiar to the open element on a FIRK but I also kept the part that goes to the fender. This should provide air for instant throttle response and also still push some cold air to the filter.

Stock my truck would not spin a tire since it has 3.08 gears. After this mod it is 100% better than before! The acceleration is much better, it pulls through the rpm range much stronger. It will also REALLY spin the tire from a dead stop. I'm very impressed. Changing the muffler was great but working on the airbox has made all the difference. I think you gotta do both changes to get the full benefit. Now I need to get the K&N. Thanks for posting the pictures ShaneM007.

I tow with my '98 Expy, can't wait to do the exhaust and airbox mod on it! I also plan on chipping the Expy, so this thing should really improve.

 

I put on a K&N fipk first, then did true duals with glasspacks and 2.25 pipe. They do work well together, but once I chipped it? Big difference,,,98