Catless downpipe for Alfa Romeo Giulietta (940) / Mito (955) / Fiat/Abarth Punto/Grande Punto/Punto Evo (199) / Bravo (198) / Lancia Delta (844) — TA Technix

The downpipe is the pipe that descends from the turbocharger. This is where back pressure builds up: the turbine has to expel the exhaust gases through a narrowed section and often a catalytic converter. Widening it frees up the turbine, allowing it to build boost earlier and more decisively - this is the exhaust modification that is felt most on a turbocharged engine.

What changes behind the wheel: response. The turbo takes less time to spool up, and the power continues higher in the rev range. On a remapped engine, this is the part that allows the ECU to deliver what the tune promises; without remapping, the ECU compensates and much of the gain remains untapped.