The benefits are two fold. The ability of your engine to expel combusted gases increases. Increased airflow gives your engine the potential to make more power. Remember that the power your engine makes is a function of how much and how efficiently it can combust the air/fuel mixture.

The second benefit of an exhaust system is the great sound they generate?in other words, your MINI won?t be mistaken for the Toyota ECHO. There are usually two types of exhaust "systems" for the MINI. The difference lies in where the exhaust system starts.

Muffler ? Replaces the very restrictive factory dual mufflers. This is a simple modification and you can expect small power gains?in the range of 4-8 hp.

"Cat-Back" (replacing from the Catalytic Converter?Back to the tailpipe)

A "cat-back" exhaust system connects directly downstream from the factory catalytic converter. The larger than factory tubing then runs to less restrictive mufflers.

Exhaust noise is louder, but sounds more powerful and purposeful.

Note that since the low cost, restrictive factory catalytic converter is in the exhaust manifold/header (where the combusted engine gas leaves the cylinders and is collected and sent to the exhaust) that more power can be gained by changing out the header for a ?complete? exhaust system that includes a high flow cat.

Expect to gain 10-18 hp (with the high flow header) and similar torque figures.