Varies from car to car.
I believe it's because you have the resonators in. They act like a "pre-muffler" to keep the tone down. removing these would then make your exhaust louder. You may want to keep them, however, in case you don't like the sound afterwards and can re-install them later.
Google: "Parametric Excitation in Frequency Resonators".
The SRT-4 exhaust will fit, but it will need to be cut and re-welded near the front of the car where it goes to the exhaust manifold. In other words, it will take a bit of custom work and extra tubing, but the exhaust can be made to fit. The exhaust also does not sound very good on a stock neon since it only has resonators and no muffler.
The actual structure
The exhaust pipes in automobileexhaust systems are designed as acoustic resonators that work with the muffler to reduce noise, by making sound waves "cancel each other out"[1]. The "exhaust note" is an important feature for many vehicle owners, so both the original manufacturers and the after-market suppliers use the resonator to enhance the sound. In 'tuned exhaust' systems designed for performance the resonance of the exhaust pipes is also used to 'pull' the combustion products out of the combustion chamber quicker. (From Wikipedia)
The exhaust pipes in automobileexhaust systems are designed as acoustic resonators that work with the muffler to reduce noise, by making sound waves "cancel each other out"[1]. The "exhaust note" is an important feature for many vehicle owners, so both the original manufacturers and the after-market suppliers use the resonator to enhance the sound. In 'tuned exhaust' systems designed for performance the resonance of the exhaust pipes is also used to 'pull' the combustion products out of the combustion chamber quicker. (From Wikipedia)
Your vocal chords.
resonators
Resonators in your body are located in your head neck and chest cavity, oral nasal and phearyngeal cavities.
The speech resonators are three: 1. Nasal (Nose) 2. Oral (Mouth) 3. Pharyngeal (Throat) (see the related links below)
"Resonator" usually refers to the Exhaust system. A resonator is a piece of tubing that is slightly larger in diameter than the rest of the exhaust pipe. It is usually located after the catalytic converter, and before the muffler. Vehicles can have multiple resonators. They also usually have some sort of sound deadening material inside. The name resonator would lead one to believe it makes the exhaust louder, but it is actually there to reduce drone and make a quieter exhaust tone. Resonator can also refer to a chamber in the intake system of the car that serves the same purpose as a resonator in the exhaust system.
The tubes are used as resonators.