You can have great sound and speed at the same time. You are just doing it wrong. You have a car with around 108HP and weighs some where around 2100 lbs (give or take a few pounds). 400 lbs is alot of weight for 108hp. You can have a fst car with a great system you just need the right set up. Performance header, intake, wires and exhaust? What I have learned from this site is, if you want a fast civic you need to do an engine swap and beef up THAT engine.

Now ive been in a few fast cars with good systems, It depends on the car. My friend has a 2004 Subaru STi, he has a banging system. Lets just say you cant sit in it too long with the music up. Now the last time he had it at the track hes runnung a 12.86 1/4 mile. That was after minor upgrades like what you have done with your SI. Recently he upgraded the turbo, fuel pump, injectors, and CAI. Im sure the numbers will be impressive. He has a custom set up in the trunk, not sure how much weight though and he is running high 12's.

What it comes down to is that a car with 108HP and a few bolts on and a extra 400lbs isnt going to be quick. With that car I suggest you re-think your set up or get a whole new engine setup.

Like I said before, im still new to the Honda scene. I'm sure someone else could give a better explanation than me. I just figured I try to help out. Good luck man