Cat-Back Systems

A cat-back system replaces the exhaust from the catalytic converter backwards: the intermediate pipes, any centre silencer, the rear silencer and the tailpipes. It leaves the catalytic converter and the engine’s emission parts in place, which is why it is the usual first exhaust upgrade. On cars with a petrol particulate filter, the equivalent is a GPF-back system that starts behind the filter.

Systems here are made for specific models and engines. The title gives the model, body style, engine and years, which is worth checking carefully, since the saloon and estate versions of one model often take different systems. Beyond fit, the choices are about sound and appearance:

• some systems come in resonated and non-resonated versions, the latter louder;
• tailpipe layouts run from single to twin and quad exits, with the tip size in the title;
• on a few, vacuum or electronically controlled valves change the sound on demand;
• Duplex systems run two pipes from front to back.

Fitting is usually a bolt-on job, but old exhausts are often seized, so have penetrating oil and new clamps ready. Use a new gasket at the joint with the converter, replace perished rubber hangers, and align the system before tightening so the tips sit straight in the bumper. On cars with valve control, make sure the new valves are connected. Louder systems can exceed circuit noise limits, so compare the system with the events you plan to attend.