Took me a little over 2 hours to install. Instructions were clear. Looks great. Don't notice anything at idle or normal driving. But once you put your foot down it comes to life and sounds great. Not sure about horsepower as car is pretty quick already but I love the much added growl it gives when you ask for it. No regrets. For the price it is a must.
As others say, this really was a pain to put on but it is worth it. For some reason, the hose I received didn't fit so I had to purchase a similar one at an auto shop. I haven't noticed any change/increase in gas mileage. No other complaints besides that. Sounds great. I am very happy about this purchase.