The first two types, catback and axleback exhaust systems, refer to sections of the entire exhaust system.
Engine Exhaust Ports on Cylinder Head
- Exhaust Manifold
- Pre-Catalytic Converter (optional, depends on design)
- Catalytic Converter
- Intermediate Piping
A "catback" exhaust system refers to the section of the exhaust from the back of the "cat", or catalytic converters, to the tips. Sections 5 and 6.
An "axleback" exhaust system refers to the section of the exhaust that is physically located behind the rear axles of the car. Most exhaust system designs have only the mufflers in this area, so section 6.
These two terms are use most in the aftermarket industry, Replacing the mufflers with "sport units" which do not damp the noise as much and may modify the pitch of the exhaust note are designed to give a more "sporty" and "aggressive" sound, usually just meaning loud. With catback systems, The intermediate piping can be viewed as excessively restrictive, so new plumbing that is wider and has less sudden bends are used to reduce exhaust backpressure.
Both a catless exhaust and a straight pipe exhaust refer to the removal of a catalytic converter in an exhaust system. In short, it is an otherwise normal exhaust system, but with 3 and 4 removed, with more piping to compensate. Catalytic converters are an emissions system that is fairly restrictive: its removal reduces exhaust backpressure, increases the engine noise heard, and causes your car to pollute the air with more severe gases and compounds.