The best replacement for straight pipe is flowmaster.

The best alternatives to straight pipe are rated as following:
★★★★★  flowmaster
★★★★★  muffler
★★★  glass pack
★★★  cherry bomb
★★  resonator
★★  performance muffler
★★  cat back
★★  downpipe
★★  catalytic converter
★★  glasspack
★★  exhaust
★★  h pipe
★  bent pipe
★  curved
★  muffler diesel
★  test pipe
★  super 10
★  high flow cat
★  catback
★  x pipe
★  stacks
  bent
  turbo back
  cherry bomb extreme
  exhaust system
  mufflers

Your alternative for straight pipe is not listed? Suggest!
Speaking about straight pipe, one probably shouldn't forget about resonator.

Other search terms related to straight pipe and their ratings are:
★★★★★ resonator
★★★ catalytic converters
catalytic converter
You have in mind a companion for straight pipe and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of straight pipe in all years. Click on graph for more.
straight pipe
flowmaster
muffler