Decided to follow through on something unique and modify the stock muffler plus share the results with everyone. I’ll post photos of the modification stages below. I have all kinds of before/after videos recorded on my phone as well and if I can figure out how to post those I will do so. Just keep in mind you’ll likely need headphones to hear the differences and the recordings aren’t a true 100% representation of what the car sounds like in person.
For the design: Essentially there’s a solid pipe welded from the inlets to the inside outlets where the valves are. Those pipes then each have an H pipe that connects to the unmodified center of the muffler. The opposite end of the center pipe, where the H pipe connects, is open and dumps into the outside chamber where the outside outlet pipes have a perforated pipe welded to it. The perforated exit pipe is wrapped with stainless steel scouring pads for sound deadening and to prevent any of the ceramic fiber insulation from being blown out of the muffler. The insulation is layered on the bottom of the muffler below the height of the crossover pipes in the middle and at the top above the crossover pipes so exhaust flow is not blocked. More scouring pads are packed in the middle to help with sound deadening and to keep the top layer of insulation from falling down and blocking the crossover pipes. When valves are open the exhaust will essentially be straight piped with some sound escaping through the H pipes. Most of the exhaust will exit via the 2 inner outlets. When the valves are closed all exhaust gasses will be routed through the H pipes where all the sound deadening is and exit via the 2 outer outlets. The insulation is rated for 2300 degrees so heat isn’t an issue and the scouring pads are stainless steel so they won’t rust or have issues with heat. Exhuast mods to the car are: Catless Tapout downpipes, Xpipe delete, stage 1/Mace cams and blackwing burble tune, however, the burble tune was removed after this modification.
Result: I’m happy with the outcome. No more tin can tone, it has a much more deep/bass tone to it. The valves work fantastic actually, I was shocked at how functional they are. Valves closed is as quiet as stock was and maybe even quieter honestly. In the cabin tour mode would be tolerable for anyone and you’d never know the muffler was modified other than the deeper tone. Valves open has a muffler delete tone but the sound level is lower than that. Valves open cold start is more aggressive than the stock muffler valves open due to the deeper tone and increased loudness. You definitely hear the exhaust more inside the car while accelerating with valves open now but that only occurs in gears 1-4 because the valves close in gears 5-8 (with the stock calibration). Once the valves close the car is silent just like the stock muffler was and just like tour mode is now after the modification. I would say inside loudness while accelerating with valves open in gears 1-4 is twice as loud as previously, maybe even a tad louder. I don’t find it annoying because it’s exhaust noise while accelerating only and absolutely no drone while cruising. When those valves close in 5th gear you definitely know it, the difference is night and day. Valves open vs closed is now a much more pronounced difference than stock was. Valves closed basically stayed the same but valves open got louder with a deeper tone. I will probably modify track mode to have the valves open all the time in all gears just to see what the drone is like and to have a full “race mode” for when the time calls. The only other thing I may try is putting an H pipe where the factory X pipe was. Currently I have straight pipes there, maybe an H pipe would refine the sound a little more. Overall this is a great mod in my opinion for 2 reasons specifically: (1) if you’re looking to retain a stock like quiet/tour mode while also having a similar mode to a muffler delete that WON’T drone at all when cruising (2) you’re looking for a deeper tone and don’t like the tin can tone the stock muffler has. Also remember the CCM can be licensed with HPtuners so you can always further customize the valves to open/close to your liking. This is a big advantage to this setup because you basically have a loud mode and a quiet mode, there’s not really anything in between or average now. So say you want a more aggressive cold start but don’t want any additional cabin noise when cruising, you can do that. Just set the car up to have valves open in park and then valves closed in all other gears. Be a creative as you’d like, Just keep in mind modifying the CCM will cost $150.
For price: My exhaust guy charged me $340 but gave me a break on the labor because I did some of the work with him. He said welding the muffler case back on took an hour alone because the metal was thin and would melt away if he went any faster. I bought way more insulation and scouring pads than I needed but that cost $120 (probably should have been about half if I didn’t over buy). I specifically got two packs of 100 gram stainless steel scouring pads made by Brheez and there’s a million different thicknesses and sizes for the ceramic fiber insulation. I got 2” thick by 24”x75”. We used a good amount of the scouring pads but hardly any of the insulation. 2” is thick and we ended up ripping most of it in half to pack it in. Just to use an easy number….For $500 or less depending on how much material you buy and labor costs…I say this is an economical and good modification if you’re looking for a deeper tone exhaust that is also louder when you want it to be.
Side note: I do NOT recommend the blackwing burble tune with this modification unless you want to sound like you’re shooting off fireworks on 4th of July. The burbles now are full on crazy obnoxious back fires at higher rpm (4.5 and above in particular). Additionally I added 4” exhaust tips which should have been the factory size. The stock size of 3.5” or whatever they are always looked too small to me for the bumper cut out they sat in. Summit racing sells Jones Exhaust JST139 tips that have the perfect size inlet, same length as stock and made of stainless steel so they should last. You should just be able to saw off the factory tips and weld these right in place with no other modifications. Best part was all four tips were about $100 including shipping. Thanks for those who tuned in and took the time to read all this. Hopefully I’ve peaked someone’s interest and maybe the next guy will create something even better than I did.