how to get outside nise out?

hi, i posted this post in integra before but i think here i can get better help:) ok so first here is my problem: im driving 92integra with aftermarket muffler and it sounds really cool but not for a long time lol so what i want is to make my car as quite as possible inside. so thats my main goal! but i want to keep my muffler lol so dont say to cahnge it back to stock one:)

im a new at this, actually first time and did some research so here are my plans: cover all car with some deadener mats( from roof to flor) than apply couple coats of edead liquid material ( if im not wrong i think its v3, in blue or black color) and all empty space between plastic panels and body fill with foam.

now what you can say about it, cuz as i sad im new in that. and how much of sq ft of mats ill need about and gallons of liquid staff .

and if any other advises please let me know, anything to help to reduce outside noise

oh and some guys told me to put extra coat of undercoat uder the car

all of that stuff will help ...... killing the roar from an exhaust system will a lot like killing the rattles from a loud stereo. I do hope you know that this procedure you are proposing will be fairly costly, time consuming and could add like 50-100 lbs to the car.

UNdercoat wont help with noise. You should be fine with just sound mat. The spray would just be dead wait.