The best replacement for straight pipes is mufflers.

The best alternatives to straight pipes are rated as following:
★★★★★  mufflers
★★  x pipe
★★  glass packs
  glasspacks
  open headers
  baffles

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

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



Google Trends

Scale is based on the average worldwide traffic of straight pipes in all years. Click on graph for more.
straight pipes
mufflers
x pipe