Did you actually install headers on your 2.5l? It seems to be common consensus that the factory 2.5 exhaust does not benefit from any changes as it is already non-restrictive, but I have seen figures which showed 525's which were factory equipped with cats saw as much as a 4hp loss in comparison to those not equipped with cats. IIRC, even adding actual headers does not necessitate exhaust mods. I think in the 525's case, it's all for bling's sake.Originally Posted by alexander525
IMO this is the difference between buying a cheap economy car which can actually benefit from even the simplest of mods and buying a factory fast car.