Which pipes give the best performance?

[stooj]

I hear other people talking a lot about how their pipes give them better performance. But then they say that when they put new pipes on their mileage actually goes down.

What do you mean when you say "performance?" Horsepower? Torque? Sound?

 

[jonny oz]

performance, while talking about exhaust systems, generally refers to torque and horsepower. sound is subjective, and not a factor when talking about performance exhaust.
the exhaust systems that will give the highest hp/tq numbers are 2-into-1 systems, such as D&D, supertrapp, thunderheader, to name a few.