This downpipe replaces the standard pipe with cat. Better transistions, increased inner diameter and removal of the cat result in a power increase over the whole rev range. Faster turbo spool and for remapped cars also a significant increase at the upper rev range. Very good value for money! Fits the Alfa Romeo 156/147/GT and Fiat Stilo 1.9 JTD euro 3 (115/140/150 HP, 2001-2005).