2004 V6 Mustang

My car has this Flowmaster Cat-Back Exhaust on it and at low RPM's it does sound like a V8, at higher RPM's it will get a little high pitch but it still has a nice tone to it. I've actually pulled in to parking lots and had people ask if I have the PI 4.6 or not, I just laughed and said nope it's a six cylinder.

To improve the acceleration first I'd make sure that your car is in good operating condition, if you don't know when your spark plugs were last replaced then now may be the time to do so. Also it was recommended to me that I should clean my MAF with MAF specific cleaner, I did and difference was extremely and immediately noticeable, my car had much better throttle response and just seemed to run better in every respect.

yea I have the Flow Master 40 series on and I have been mistaken for GT every time......provides nice deep tone all around and really growls when I lay into it...
as for responsiveness make sure shes tuned up and running at peak performance I did a cold air intake on mine I can feel a little change as dose it sound a little nicer too.