I've seen a couple posts and sigs with people using a smaller downpipe than exhaust (ie. 2.5" DP and 3" exhaust). I'd think the optimum would be to have the DP be the same size or bigger than the exhaust, or is that not right? More to the point...I've got a 2.25" cat-back(possibly with test-pipe) now and will soon be going turbo with a 2.5" downpipe. Is this a good DP for the exhaust I have?

 

Most guys won't have a full 3" downpipe because it interferes with the A/C compressor, so you would have to remove that to go full 3" (at least that's what they say, when I took a look down there, I personally didn't think it would interfere).
Yes, full 3" is idea if you can do it, but a 2.5" into 3" downpipe with 3" test pipe and exhaust is almost as good, and probably all you need.

 

AHH, that makes sense about the AC...I'm still not 100% how I'll be able to keep mine when I do my install. I think I might have to go to a slimline fan, at the least. I'm planning on going ghetto with the STD civic manifold and a T25...any idea how far that will stick out from the block? I've got about 7" with the fan installed between the core and the block, and 10" if I take it off and get a slimline in front of the core. I was thinking it might be possible to have the compressor on the passenger side, like the Apex'i kit, among others, so I can keep it away from the compressor, any ideas if this works?