Of course, the air and fuel going into the engine, and the spark that ignites it are only the beginning and middle of the process. Horsepower and torque are also affected by how easy it is to get the smoke out of the engine that is left over after the gas and air explode. After the piston has been pushed down by the explosion in the cylinder, as it comes back up it pushes the smoke from the explosion out the exhaust valve and into the exhaust system. If the smoke can’t get out easily, that puts pressure on the piston, making the engine work harder.
As a result, performance improvements also can be made by improving the exhaust system. In the MINI, the exhaust system consists of “headers”—those pipes into which the exhaust gas flows after it comes out of the “head”—the top part of the engine. From the header pipes, the exhaust gas flows into a catalytic converter (sometimes called a “cat”), which is the essential element of the modern emission control system that captures contaminants rather than letting them flow out of the tail pipe.
The exhaust gas flowing out of the cat is piped through the muffler to reduce noise, and from there out the tail pipes. The muffler, and the pipes into it and out of it to the tailpipe are often referred to as the “cat-back” part of the exhaust system.
If we can make the exhaust gas flow more easily, we will increase the power that the engine can produce. This can be done by replacing the factory-designed system— which was engineered to a budget and designed to reduce exhaust noise as much as possible—with a more efficient Mini cooper cat-back exhaust system.
A variety of different types of cat-back systems are available for the MINI. The differences among them are cost, installation convenience, performance, and—very important to many drivers—the exhaust tone. Exhaust systems, like the curry in your favorite Indian restaurant, can be ordered in mild, medium, or aggressive form.
Three different systems are good examples of these differences. The least expensive we’ve found, at about $700, is a two-piece system designed by MiniMania with a single muffler and large-diameter tailpipe outlet.
Though this system uses factory-mounted installation points, it uses a different design than the original, incorporating two sequential mufflers, making it easy to install and weighing approximately 20 pounds less. The system produces increased performance, and has a nice medium-aggressive sound.
Borla, the well-known exhaust company, makes two different cat-back exhaust upgrades for the MINI. Both have a different and slightly more complex design that incorporates two separate mufflers exiting through twin tail-pipe tips at the rear, similar to the original system. The basic system offers good performance improvement, while maintaining a factory-like tone, while the “Sport” cat-back offers slightly better performance and incorporates different mufflers to produce a much more aggressive tone. Both are priced at about $800.
These Mini Cooper cat-back exhaust systems aren’t difficult to install for anyone with a good set of wrenches and a little garage experience. However, if you don’t fancy putting your MINI up on jack stands and crawling under it to make the changes, a good muffler shop can make the substitution in about an hour or two of shop time.