Removing inner down pipe liner.
 

I'm looking to go full 3" on my exhaust when I do the K27 upgrade. My cost-free solution for accomplishing this (for the cat-forward section, anyways) is to remove the inner liner from the stock DP, and then weld it back together. I would then wrap it with that blanketing stuff, prior to re-installing it, to help keep it from cooking things nearby. Would anyone wager to say, whether or not this might be feasible? Does the inner liner go all the way from the turbine flange to the front of the cat?

you'd also have to somehow bore out the end flanges to 3" for this to work.

on second thought, i think the outer wall on the stock downpipe tapers down to 2.5" to fit the flanges so i'm not sure if this is feasible.

i'm also not sure if the outer wall is actually 3" either.

I figured that, about having to bore out the end flanges. But I don't think that the turbo end flange needs to be altered, because the turbine outlet (#8) is only 2.5 inch, right? If if tapers down before it gets to the cat, I'll just have to cut it at the point that it starts to taper, and add 3" pipe to it from there. And I'm not sure it's exactly 3" OD, either, but by the looks of it, it's close enough call it 3. At any rate, it looks like I'm going to have to wing it, once the big upgrade project gets under way.