Im thinking about going to a local exhaust shop and doing a muffler, resonator and secondary cat delete. Is the car gonna run fine with all this or am I going to need a tune? What kind of power gains can I expect? And how bad will this mess up my warranty?
I did pretty much everything you plan on doing aside from the resonator. I have a complete custom exhaust setup, I didn't pay $2000 for downpipes and a catback. I paid around $640, just make sure you bring it to an experienced exhaust shop. I had people from different age groups tell me it sounds fine, not too loud, not too quiet. You will also get a nice burble when you let off the throttle and just cruise.
The stinger already comes with 2 high flow cats right before the down pipes. Change the down pipes since there are weird oval sections at the bottom, not sure why they did that but changing the diameter mid exhaust never seemed like a good idea. I removed the secondary CATs, just make sure where ever you live allows you to run high flow CATs. If not you would have to keep the secondary CATs, that's probably why Kia added them to begin with.
The stock exhaust had something that resembled an X pipe but it's not real. It's just a metal bar that is welded to hold the two pipes together. Adding an X pipe or H pipe in the setup would be beneficial. Really depends on what kind of sound you want coming out of it and where you want the improvement. I think H pipes were better for higher RPMs or something like that and X pipes were better for lower.
Keep the factory resonator, I kept my factory resonators since they don't have a performance impact. The X pipe alone will add a nice sound to the car, a nice deep rumble. If you want to be safe and reduce the possibility of making too much noise, Magna Flow makes an X pipe housed in a muffler. That adds weight and bulk so I didn't bother, I just put on a standard X pipe. Not sure if they have an H pipe in a muffler.
You can delete the rear mufflers, there are some weird twists and turns in the pipes that go into the muffler. You can have the shop make a more straight pipe design, just make sure you follow the stock mounting points and curves to avoid conflictions. Also try to use the stock mounting rubber, that will greatly reduce any drone but not all. That's just the nature of removing parts that are designed to keep the car quiet.
If your stinger has the active exhaust functionality, just make sure they retain that. They can simply just cut off the 4 pipes at the end and weld on a Y pipe to where the muffler used to be. I don't suggest you only keep the small section of the active exhaust. I have seen videos where they cut off that small section and welded it back on, the rattle sounded like crap. This will also help you avoid engine codes.
As far as the tune goes, you really don't need to get one to see any benefits. A tune will obviously give you more gains, but it's only one piece of the puzzle. Everything you do to your car has a cumulative gain. For example don't expect to push 10 PSI over stock and get major gains, you'll need to upgrade the intercooler too or your IAT's will just eat up all your performance.
I personally haven't put my car on a dyno because it's really hard on your car. I wouldn't be able to tell you how much power gain there would be from just doing the exhaust. There are shops out there that show videos of a dyno run before and after an exhaust change. They usually get from 15WHP to 20WHP gain by just changing the exhaust. You could possibly gain more since usually these shops still have some kind of muffler and secondary CAT. Honestly though the HP number is just a bragging tool these days, as long as you like the way it drives it doesn't matter.
The exhaust system doesn't usually have any warranty to begin with. Kind of like your brake rotors and brake pads. Besides I see you're in the US so you have the Magnuson-Moss Warranty Act on your side.
Remember, your stinger is your stinger. I'm sorry you wanted information and people just blasted you with their opinions. I have actually done what you're planning to do and if you would like a video of what my car sounds like I would be happy to take some time to record something. The car runs perfectly fine and from what I can tell the sensors are before the downpipes. The car won't throw any engine codes unless they ark weld your car to death or mess up the active exhaust motors.
