I've narrowed it down to two: Helix catted or Cobb catted. Everyone EVERYONE keeps saying go with Helix, because it is cheaper. My concern is that since I plan to only swap DP and stick with the stock back exhaust, the flat flange on the Helix will leak. Worse yet, I read an actual post on NASIOC (or i-club, can't remember which) where Dan Harman (Harman Motive) said that one of the key reasons the heatshield welds on the STI UP fail and rattle is due to replacing the stock donut/flex joint with a flat flange. Is this just BS?
if i was you i would add another dp to list.. it is the INVIDIA CATTED DOWN PIPE. it works with all stock parts, no leaks and is a great proformance part just like the helix or cobb... it is great with most cat backs.. with my greddy evoII i have no complants.. also it cost as much as helix or a little bit less depends.. but it fits all exhast parts.. with no problem.. research INVIDIA Catted DP.. u will find your most answers with mic from sakari MP
+1 for the Helix... Really don't think you can go wrong with it. I haven't had any issues with the up heatshield rattling. Certainly not saying what Dan's saying is BS, just haven't run into that problem.
I think the main concern OP is having is the joint in between a 3" flat flange and a 2.5" donut flange. Helix and Invidia i believe uses the 3" flange so yes both will see the same mating concern What i dont understand is why is the STI UP heat shield cracking due to the donut joint ? - Vibration ?
yeah its the extra vibration the cracks the welds on the up heat shield. ive only seen this happen once though and it was on an invidia dp knock off that was huge. it almost touched the firewall when installed. had to reroute the ac drain hose so it wouldnt burn.
I just ordered the Helix catted and it's on it's way! For me the choice was between Helix and Cobb since they both have the se`condary O2 bung for wideband tuning. The Cobb had the donut that I didn't want, and was more expensive so I ran with the Helix. Finding a shop with the Helix in stock was another story, and I ended up getting mine for $399 shipped from dchmotorsports.com out in Temecula, CA