If you have enough money buy a good blow off vavle and drag exhaust system ..
Don't buy any exhaust with bad specifications ..
A big single muffler is good for performance because the gases of the engine will get out faster than if it's subordinated ..
Wanna see Examples ?
That one made for performance
it does weigh 4.5 kilogram while this one is made for the show and the performance . It weighs 12kg
I see a lot of owner of 3si buying a dual exhaust systems !
I don't know why but I think it's probably the price ..