The best replacement for catalytic converter is muffler.

The best alternatives to catalytic converter are rated as following:
★★★★★  muffler
★★★  oxygen sensor
★★★  resonator
★★★  test pipe
★★★  straight pipe
★★  o2 sensor
★  no catalytic converter
★  sensor
★  fuel pump
★  transmission
★  aftermarket
  torque converter
  exhaust leak
  oem
  direct fit
  high flow
  exhaust

Your alternative for catalytic converter is not listed? Suggest!
Speaking about catalytic converter, one probably shouldn't forget about o2 sensor.

Other search terms related to catalytic converter and their ratings are:
★★★★★ o2 sensor
★★★★ california emissions
★★★ manifold
★★★ straight pipe
★ oxygen sensor
★ o2
★ exhaust
sensor
You have in mind a companion for catalytic converter and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of catalytic converter in all years. Click on graph for more.
catalytic converter
muffler
oxygen sensor