Im thinking about upgrade the exaust of my car, I alredy have the y pipe from WSP, I will make a custom 2.5 B pipe and will and a muffler mabe from mangnaflow, but im not sure what size should I get it. I want it to be not too loud, I will and a resonator to keep the sound a little down, magnaflow have diferent sizes 4x9x14, 5x9x14, 5x9x18, 5x11x18, 5x11x22, and some more.
the question its what size should be fine?
The smaller its the muffler the louder it its or if it´s bigger its louder?

Thanks in advance