just wanted to know what where the good/bad affects of running my 2000si axle back

 

You will probably lose some backpressure, so your car might feel slower when you start going.

 

why would ppl run they're cars like this then...i kno to individuals who have pretty quick cars and the have intake and run without the muffler

 

You will gain velocity in the air movement without the muffler choking the system, esp. with stock exhaust pipe diameters, mufflers were intended for economical reasons not HP. You will [robably notice maybe a 1-2hp difference in the top end of the power band, and of course more noise. Is it worth it to be illegal... probably not.