Length

• Cat-back exhausts are longer than axle-back exhausts. A cat-back exhaust replaces all the piping in front of a catalytic converter, which is located near the front axle of a car. An axle-back exhaust replaces all the piping located in back of the rear axle; this is usually the muffler and a small section of the exhaust piping.
  
  

Horsepower

• A cat-back exhaust, when installed with an air intake, can increase a car's horsepower by five to 10. An axle-back exhaust is usually installed to change the sound and look of a car. The horsepower increase of an axle-back exhaust is minimal.
  
  

Price

• Cat-back exhausts can range from $300 to $500 as of September 2010. Axle-back exhausts range from $150 to $400. The pricing is varies between cars and manufacturers.