IMO, i think these sound stock... maybe a little louder if i squint my ears.

I expected a huge change in sound, but they don't sound that loud at all... don't know if there is a huge hp gain, but I sure smelled the new cats burning in though. If they give me the HP gains as advertised, two thumbs up!

 

Change out the stock exhaust and you will hear a difference. And yes they will give you gains.

 

Yeah. They made my Z louder. And it actually put my exahaust to good use (performance wise). Without them, I just had a loud exhaust.