My friend has one that he hasn't used and wants to sell it to me. He told me that i can bolt it onto my factory exhaust and it will make it sound louder with some power gains.

Is this true

 

he has a y pipe

 

I think you mean the test pipes. The pipes that replace the Cat's. Also known as race pipes. Stillen doen not make a Y-pipe. The test pipes will give you a little more sound and some power gain. They are a pretty easy install too. Brand new they cost about $300.