I am guessing by your name that you have an '01 if so the big one under the passanger seats is going to be the muffler and the smaller one at the tail pipe is the resonator ( basically a second muffler just to keep it quiet ). You can get rid of the resonator with out getting a CEL here are some pics of my '02. I just put in a Flowmaster 70 series DI/SO ( its almost the same size as the factory muffler but nice because you don't get a lot of drone inside but you can still tell it is a V8) getting rid of the factory Y and got rid of the resonator and it made a huge difference. Let me know if you have any questions I did have to put in a provision for the pass side rear o2 sens, but found that a ford spindle nut works perfect for a o2 sensor bung.
