Between the turbo, intercooler and engine, air flows through pipes. The original ones are often made of rubber: under pressure they expand, absorb part of the pressure and delay throttle response. At high pressure, they eventually pop off, and the car goes into limp mode at the worst possible moment.

On the intake side, the original turbo inlet pipe is often narrowed for noise-reduction purposes. Enlarging it allows the compressor to breathe: a gain that is especially noticeable on an engine that has already been remapped.