Hey, I've been lurking trying to find more info before I pull the trigger on the DT headers, plus any extra required items for installation and use. I have an 05 V8 with the Borla CatBack dual exhaust. I HAVE to be able to pass CA state smog checks for my Oregon registration renewals. If I am understanding this, there's long tubes and short tubes, and the additional question if you want a Y pipe, and the potential for removing CATS? I just want headers, and no check engine light, and pass smog if that's possible with my setup. I'll do the Y pipe if necessary, but I thought I had one from my exhaust system.
Either LT or ST Headers you can remove the primary cats.
The LT are 100% bolt-in. They attach to the engine block, then conenct to either the factory y-pipe or the DT/URD aftermarket y-pipe.
The ST are designed to be welded to the top of the OEM primary cat, but you don't have to if you don't want. You can have your fabricator weld in straight pipe to then connect to the y-pipe of your choosing.
If you're planning on running no primary cats (I elected to buy some really nice performance cats because I didn't want to stink like hell, link in my signature), the decision comes down to how easy you want the install to be and to where you want most of the power gains. LT will be higher in the RPM range while ST will be down low. I tow somewhat often, so I prioritized the low-end power over mid-high end power. It's a truck, not a track car.
Does CA do exhaust inspections beyond just looking for codes? Visual or exhaust gas sampling?
If they just look for codes, then all you need are the LT headers and the Rear O2 Simulator. You can run whatever y-pipe you want. If it were me, I'd spend the $400 on the DT y-pipe and get rid of OEM y-pipe and cats. The DT Y-pipe has resonators, not cats.
But if you want to keep the secondary cats to at least run KINDA clean, you can. But I would look at welding in a section of pipe to replace the crushed portion of the y-pipe where it crosses under the Transmission. Super restrictive there and I'd want it gone if it were me.
Little long winded, but boils down to below (assuming they're only looking for codes).
Running LT: all you need are the headers and the URD O2 Sim (assuming the inspector only looks for codes at inspection, if they look for more, I'd run ST + cats, with a catless Y-pipe).
Running ST with cats: Headers, then decide on what you're running for primary cats, and fabricate connection to y-pipe if not reusing OEM primary cat.
Running ST no cats: Headers and O2 Sim, and fabricate to y-pipe of choice.
If the inspection is more thorough (visual and/or gas sampling), I'd recommend the shorties, the cats I have in my signature and the DT y-pipe.
Hope this helps.
