Things are never as straightforward as you first think. I recall on my '02 the stock catback was 2.5", I assume the same is true with the '09?

So if I go with an aftermarket DP like the Cobb or Invidia but want to keep the stock catback, I assume I'll need some hokey adapter to fit the 3" pipe onto the 2.5" catback, or else get a DP that tapers down to 2.5" to begin with (ugh)? Any major drawbacks with either approach?

Makes me think the "stage 1" route is the right way to go until I have some time to edumacate myself about the best route on a DP?

 

Ah, yes, but there is a very simple fix. There is an adapter that you can buy for about $45 that allows your 3" downpipe with a flat flange to match up perfectly with your 2.5" catback with a donut flange. You can get it here.
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Box vaporizer