sidepipe
An exhaust pipe which exhausts to the side of the vehicle.
sidepipe: exhaust that exits through the car's flank
A sidepipe is an exhaust outlet routed along the side of a vehicle, typically exiting near the rear wheel well rather than at the rear bumper. The pipe runs the length of the chassis, visible and exposed, rather than tucked underneath. This configuration was common on American muscle cars and performance vehicles from the 1960s onwards, where it served both functional and aesthetic purposes.
The routing requires welding or clamping the pipe to the vehicle frame or body, often with heat shields to protect the side panel from radiant warmth. A typical sidepipe diameter ranges from 2.5 to 3.5 inches on standard performance cars, with dual sidepipes being more frequent than single installations. The exit point sits roughly level with the door threshold, meaning the outlet is far closer to road debris and moisture than a conventional rear exit would be.
Why the design persists despite drawbacks
Sidepipes offer genuine advantages in certain applications. They reduce backpressure by following a straighter path than underbody routing, they simplify installation on modified chassis, and they allow clearance for longer beds on trucks. The visual statement they make is intentional: the exposed pipe signals performance modification to other drivers. However, they create real problems. The side exit directs hot exhaust across the rear quarter panel, complicating paint protection and causing heat damage to trim. Salt spray and road grit corrode the exposed pipe faster than protected alternatives, and the outlet itself becomes a hazard if touched during or shortly after operation.
Sidepipes fell out of favor on street-driven cars partly because noise regulations tightened and insurance underwriters grew cautious about the exposed contact hazard. They remain standard on certain drag racing vehicles, vintage restorations, and specialty motorcycles where appearance and slight flow advantage outweigh the maintenance burden. Modern fabricators typically use aluminized or stainless steel rather than mild steel to extend the life of a sidepipe installation, though stainless adds cost and weight.