Originally Posted by Darth_Focus
The ST exhaust actually sounded pretty good. However, would the increase pipe diameter have a negative effect seeing as everything on these modern computer controlled cars are so tuned? Just wondering because you can get to a point where exhaust scavenging becomes an issue and you end up with a back flow, which is not good at all.
So far others who've had the 2.5" FSWerks exhaust for a long time haven't really had any issues with back flow or anything similar. The stock exhaust is already 2.25" directly behind the catalyst on non pzev models before necking down to around 2.0" after the first resonator.
It's been reported that there are still gains to be had on the high end in going with a 3.0" exhaust with an aftermarket exhaust manifold also, but personally I'm not looking to push things to the extreme.
The flow was pretty well maxed already for the 160 hp of the stock exhaust set up.
The only reported case of non warranty engine failure seems to have been due more to owner neglect and abuse on a car where they installed an aftermarket exhaust header without hooking up the wide band oxygen sensor and proceeded to aggressively drive the car for a period of time until the inevitible happened given the car would be running in open loop.
Since this is down stream of the emissions control equipment it should only help to evacuate the exhaust gasses, most of the scavaging effect is contained within the exhaust manifold itself which isn't changing.