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Stock muffler modified

1321 Views 9 Replies 3 Participants Last post by  BigSteamer
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.
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I created a YouTube channel with all the videos I have. All videos are clearly titled, have a description and text within the videos so you know exactly what you’re listening to. There’s a couple short Tapout Carbon Fiber intake videos on there as well. All videos recorded with an iPhone.

YouTube channel is: BigSteamer13

Here’s a link:
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Got the YouTube channel setup a littler better as this is all new to me. Currently, I got 17 videos posted documenting cold starts, revs and everything in between with different exhaust setups. There’s a couple short aftermarket intake videos as well. Videos are labeled with descriptions. My main goal is to help people as they research exhaust options for their car.

Channel name: BigSteamer

Here’s a link:
That's super interesting. There's a ton going on here, and I don't want to really give my impressions until I've had time to process your videos.

While I'm thinking this through, did you consider adding an H-pipe in the muffler, pre perforated tubes? Or does that need to be up forward in the exhaust system? Also, for those that want an even quieter tour mode and control over sound, did you consider adding another set of baffles (the walls with the perforated sides) between the straight pipe and the outer exit?

Finally, do you remember what diameter pipe you needed?
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No problem man, definitely check the videos out. I have individual clips posted in “shorts” that will play on repeat and I have regular videos in a compilation style directly comparing the modified muffler against the stock unmodified muffler. Everything is also organized in playlists so you could select a playlist and just let the videos roll. I’m a rookie with posting videos so please excuse my filming skills. All the information will be there, just might not be the prettiest to look at. I’ll continue to add videos as I can. I added one tonight with cabin decibel readings using my Apple Watch. I plan on doing the same tomorrow with cold starts in the garage. I don’t know how accurate this watch is but it’s some type of measurement. It can be used to compare valves open vs closed at least.

I did consider an H pipe where I previously deleted the factory X pipe. I asked my exhaust guy to weld a H pipe back in but he ran out of time and the way my schedule was I took the car home without the H pipe. (Side note, I found that deleting the X pipe reduced rasp as well as backfires on the burble tune). I figured I could test the new muffler as is and add the H pipe later if desired or I wanted to see the difference. Originally I thought the H pipe would be necessarily to reduce some drone and harshness plus smooth out the exhaust. I haven’t got on the highway at 70+mph yet but so far I don’t find a H pipe necessary. Unless I wanted to smooth out the exhaust but I’ll have to have someone drive the car while I stand outside to hear it.

Interior resonance with the valves closed is very similar if not the same as before the modification. That means tour mode in all gears is quiet just like it used to be. The valves only open in tour if you exceed 3500 rpm. Sport mode has the valves open in gears 1-4 only so once you hit 5th or you’re cruising the car is quiet just like tour mode. Currently I have track mode setup with valves open at all times which is basically a muffler delete and it does drone. With the valves setup this way you get a quiet mode, a loud mode and then a hybrid mode that is loud while accelerating but quiet once you’ve gotten up to speed.

As far as baffling, I eliminated those two baffles for a couple reasons. I didn’t like the tin can tone the stock muffler had and I suspected those baffles contributed to that. I also wanted to do something different than what was already there. I didn’t want to further perfect what what Cadillac already engineered, I simply wanted to go a different route with their design. The main reason I did this was to eliminate the tin can tone and I felt deleting those baffles was necessary. I have no science to back this up lol, but I can confirm there is no more tin can tone.

Also I considered having a perforated H pipe connecting each solid inner pipe to the outer perforated pipe but again that would be another step similar to the stock design so I decided against it. My concern for wanting that additional perforated pipe was to ensure the exhaust was flowing enough with the valves closed. After analyzing how small the perforations the stock baffling uses for valves closed, I can’t imagine my design is anymore restrictive. Fortunately the exhaust is flowing fine without that pipe and with valves closed. I haven’t datalogged it or anything but the car is accelerating with valves closed the same way it does with valves open. Honestly, going without the pipe may make the exhaust quieter with valves closed as well. Having the sound dump into a chamber filled with sound deadening seems more dampening than sound going through a perforated pipe inside of the same chamber. The sound waves in the pipe can stay in the pipe somewhat vs sound waves being competed forced through a dampened chamber.

I believe the pipe used was 2.5”. I know cat back to muffler is 2.75” and the four exit pipes from the muffler are only 2.25”. For that reason I didn’t view 2.5” at the very end of the exhaust a restriction.

This muffler designed as is accomplished my goals:
-It eliminated the tin can tone. It’s a much deeper tone
-I have a quiet mode
-I have a loud mode
-I have a hybrid mode
-There’s no drone unless I want that (Track/loud mode)

Maybe an H pipe or a different design could improve upon my design but I’m happy with what I got. The muffler flows good so any changes would strictly be for acoustic reasons. An H pipe before the muffler would probably only be beneficial for toning down the valve open exhaust. An H pipe inside the muffler would likely tone down valve open exhaust but could increase sound with valves closed as well. What you’re taking away from valves open could get handed off to valves closed in that scenario. Maybe that’s beneficial for someone looking for a medium quiet and a medium loud setup vs a quiet and a loud setup.

I haven’t found an H pipe necessary for valves closed mode yet. I’ll try to get it on the highway at 70+mph and see if that remains true. I also want to hear someone pull away in it while I’m outside watching. If there’s drone on the highway or the exhaust sounds harsh on the outside I’ll be adding an H pipe. I would add it where the X pipe was because it’s closer to the front of the exhaust compared to the muffler and I already know modifying the exhaust at that location does change the exhaust note. Which makes sense, Cadillac put the X pipe in that exact spot for a reason I’m sure.

Thanks for taking interest in this. I truly believe this could be a good mod for people looking for an aftermarket exhaust but not willing to pay thousands of dollars. Including labor and materials this is probably an approximate $500 mod. Considering you’re keeping the valves with this is important. Borla also has a valve system but you’re paying $3000 not including install.

Additional H pipe style designs I considered inside the muffler are pictured below


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Doing a proper sound comparison is hard, because you've gotta plan ahead to capture audio the same way before and after, and make sure that your mic settings aren't influencing the recording. Phones are bad for objective comparisons, because they automatically compensate for adverse conditions.

Here's an example of the kind of video edit we need:

This guy failed to record proper audio (his mic is being blown out), but he's got the right idea.

Your videos are all different (e.g. from the front, from the sides, etc), plus you had a burble tune in some videos and others not, so it's hard to judge fairly. If you could re-record that driveway video again it might be helpful, but it might come down to others to build on what you started.
Completely agree with you. I certainly don’t have any professional equipment or even a camera. Everything is filmed on a top of line iPhone when I’ve had the opportunity. Also YouTube could be downgrading the 4k quality and good audio they were originally recorded in. I understand some of the videos are filmed during the day, some at night, some different locations but they’re all filmed in open air environments from similar angles with the exception of closed valve modified muffler cold start compared to the stock muffler closed valve cold start. All cold starts were done with the motor cold, not back to back. All revs were done with a warmed engine. I only had the burble tune prior to the mod so that’s the reasoning for that. Post mod burble tune and no burble tune videos are both in the rev compilation video.

The videos aren’t perfect but I assure you that overall they fairly illustrate the modification compared to stock. The take away is the modified muffler has a much deeper tone than stock, the tin can type noise has been eliminated and it’s louder than stock with valves open. It sounds similar to a muffler delete but not quite as deep or loud AND (important) without drone or annoyance of a delete or any muffler change for that matter. Valves closed has a deeper tone but sound level is extremely similar to stock with valves closed.

I think the valves open cold start compilation and cabin noise videos documented this pretty well. Valves closed vs open inside the car is basically a difference of 10+dB which is huge. I’ll have another video posted today showing cold start dB in the garage valves open vs valves closed. The dB difference inside the car is similar to the difference outside of the car dB wise. The purpose of both videos is to show the difference in modes, how valves closed is and how friendly the car can be for your family if it’s parked in an attached garage. Unfortunately I don’t have pre modification measurements. I didn’t really expect to document everything like this. I’m taking the time to document everything now because I’m pleased with this mod and I believe it’ll work great for others as well.

I just simply don’t have the time or equipment to do anything much more professional than I currently am. Yeah it’s not perfect but the overall end result can be heard. If there’s anyone in the metro Detroit area that wants to check it out or film it better than my capabilities that’s ok with me.
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I understand my responses are in depth. I’ll post the highlights below for the muffler modification compared to stock muffler below. Bottom line:

-I don’t see a downside with the mod
-Valves closed is similar to stock. Valves open is aggressive like a muffler delete but doesn’t drone because the factory valves are retained.
-Valves open has a deeper sound but toned down from a muffler delete
-Valves closed is a deeper tone but not louder than the stock muffler with valves closed
-Tin can sound is eliminated regardless of valves open or closed
-This mod legitimately gives you a muffler delete type mod AND the option to keep a stock like quiet mode
-Keep things quiet like stock at all times by using tour mode
-Keep things loud while accelerating but quiet while cruising by using sport mode or track mode
-License the CCM for $150 to modify the valves anyway you want. Keep valves open constantly like a muffler delete if desired
Well guys I officially got all the videos I could think of for now added onto YouTube. Just posted a fly by type video that is the best quality and best editing I’ve done so far. Previously I was using iMovie but it was downgrading my quality. I used the Clips app this time. I had limited space to work with so speeds didn’t get crazy and I didn’t rev it out all the way but she sounded real good then quiet/drone free for the ride home.

Hopefully some of you have found this helpful and I’d be interested to hear if anyone else tries this muffler mod. Thanks guys
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