The best replacement for catback is muffler.

The best alternatives to catback are rated as following:
★★★★★  muffler
★★★  axle back
★★★  catless
★★  turboback
★★  downpipe
★  axleback exhaust
  turbo back exhaust
  axleback
  turbo back
  no catback
  straight pipe

Your alternative for catback is not listed? Suggest!
Speaking about catback, one probably shouldn't forget about invidia downpipe.

Other search terms related to catback and their ratings are:
★★★★★ invidia downpipe
You have in mind a companion for catback and it is not yet here? Propose!



Google Trends

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catback
muffler
axle back