Like what Mu Secret said; Mugen is not that loud compared to injen or GruppeM. With the injen, it's definately loud (Especially in vtec), even when you're driving normally <3k rpm, you can hear a more aggressive sound while you're driving...IMO go get yourself the injen (try source a 2nd hand one if you can...) and just to assure you, it's not just sound improvement...you gain decent improvement in performance as well...with such a basic/affordable mod...it's worth it
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