Haha...old school! I guess that I am, since my memory caused a bit of misinformation. My DC 4-2-1 in fact has a 2.25" collector, and not 2.5" as previously posted.
Along with the stock cat, I guess even upping the diameter piping won't be significant...being that Greddy's piping is 60mm (2.35"?). The collector and cat would just be bottlenecking larger piping anyway. Or would larger piping still yield some, albiet not much, benefit from the cat on back?
Been looking at HyTech's system, but that's bread! And again, if I keep the DC, which will likely be the case, there's no point in spending that kind of money, right?
While I'm still waiting on Greddy's response on the SP1 piping to SP2 muffler fitment issue, I'm now finding it difficult to decide what complete system I want to buy. I'd stick with Greddy because I like how the SP's sound, but as others have noted, I'm starting to agree about their lack of long-term durability. All the Greddy exhausts I've bought did seem to crack/leak and generally break down prematurely. Can anyone vouch for Apex'i's quality being better than Greddy's? N1 or WS...pros/cons between these two?