I'll refrain from ranting on this, but it is ridiculous how much 3" DPs are pushed onto people. I've got a 2.5" DP on my GTP and I got that on purpose. By the time a 2.5" is going to hold you back, you are in header territory. I personally think a 3" DP is useless. The stock exhaust is routed pretty bad anyway, the DP band aid can only do so much. 2.5" will help you keep low rpm part throttle response, and won't make any appreciable difference at higher RPMs. The 2.5" DP is also cheaper and you don't have to worry about flipping your sway bar. And I am not the only one who feels a 2.5" is just fine for a GTP. From Overkill's website:
"Which size is right for my vehicle?
We recommend 2 1/2" downpipes for most vehicles. If you have a GT, you'll retain your torque better. On any vehicle however, supercharged included, that is keeping the less restrictive factory cat-back exhaust or has a 2 1/2" aftermarket system, the 2 1/2" will compliment its flow better...A 2 1/2" downpipe with Powerlog will support bolt-on vehicles idealy." Emphasis added.
When comparing a stock DP with an aftermarket, you also need to keep in mind that the stock is double walled and has barely a 2" ID. So yeah, feel good about keeping it.
