Hey all,

I've got a 991.1 GT3 and I'm going through the usual dance of trying to find the right exhaust setup to meet my dual-purpose needs: at least twice weekly highway spirited driving and track use at least ten days a year. I started off with a Sharkwerks center muffler delete (CMD). It was loud but not loud enough. The cabin experience was perfectly fine on the highways, usually the worst place for aftermarket exhausts. I just wanted more noise outside and inside when I'm on the power. This setup didn't drone.

This week, I put on a valved Soul side muffler delete (SMD) and kept the Sharkwerks CMD, basically just running OEM headers with a valved side pipe. I knew this wouldn't be the final answer but wanted to hear the car like this at least once. This setup drones at various RPMs, is not dailyable, and likely requires ear plugs on the highway depending on RPM. When you want it to be loud, it sounds terrific. When you want it to be quiet, even off throttle, it's obviously impossible.

I have a few directions I could go:

• Swap the Sharkwerks CMD for a Dundon quiet lifetime center muffler and leave the Soul SMD. This could potentially kill the drone (according to the product page for the muffler on Dundon's website) and leave the car louder than having just the Sharkwerks CMD by itself with OEM side mufflers. This seems the most promising to me if the below street bundle option fails.
• Swap everything for a Dundon street bundle, which would include the street headers and the loud lifetime center muffler. I think this would be loud enough based on reading around the Internet. My concerns on this would be with cabin drone and with a pre-cat check engine light (CEL) via the exhaust O2 sensors. I've heard that, due to the placement of the cat within the street header being farther from the port, it may not heat up quickly enough and throw a CEL. Either one of these concerns being realized would be a deal breaker and I'd have to switch. Being in TX and having a 991.1, I'd be worried about tuning the motor to clear that CEL.
• Swap the muffler deletes for a catback FI or Akrapovič exhaust. This has the benefit of guaranteeing no CEL but leaves the concern around drone.
• Swap the Sharkwerks CMD for an OEM 991 GT3/RS muffler. This setup would probably drone with the Soul valved SMD. This is the cheapest and easiest, but the risk of drone and the risk of the muffler cracking leave this option pretty unappealing. Additionally, if I put back on an OEM GT3 muffler, that's weight I don't want to add back with it being steel.
• Return to my original config with just a Sharkwerks CMD. I don't want to do this because the side mufflers weigh too much and are too close to the rear wheels, causing heat management issues with the rear tires. The car oversteers most everywhere at CotA with the roll bars on normal and a shim up front giving -3 degrees of camber. I'll probably stiffen the front bar but I want to cool my rear tires and remove some weight to help with the polar moment of inertia and overall rear-end mass.

I'm looking for:

• A conversation in this thread about people's experience with any of the above exhaust configurations; and
• Anyone in DFW, Texas that has a non-OEM exhaust setup they enjoy on any 991 GT3(RS) that wants to meet up and share their passenger seat with a curious enthusiast. I'm happy to share my right seat, too, but you'll go deaf or at least get tinnitus before long.

 

i am running SW bypass with valve delete
it sound pretty good but often I envision a louder exhaust option
but then it will likely drone and wake up my neighbors so its prob smart for me to keep my current setup

 

Do you have the OEM center muffler? It sounds like your current setup doesn't drone, which may give me some peace of mind if I go with an OEM muffler.

 

I do not have your set-up, nor the options you are considering, but my experience may prove helpful.

I purchased my 991.2 GT3 used. It came with OE headers, OE side mufflers, and the GMG center muffler delete (CMD). All else the same, my research suggests that combination is slightly louder than the Sharkwerks CMD. The only significant issue with my set-up was that I had a boomy drone in the neighborhood of 2800 RPMs. Since I am not a track guy, I looked to eliminate the drone.

A local GT3 owner was selling his GMG equal-length headers with the 200 cell-per-square-inch catalytic converters, so I decided to give them a try. Four things changed after the headers were installed:

1. The exhaust was louder—no surprise—whether the valves were open or closed, but the volume was entirely reasonable.
2. The aforementioned drone was eliminated when the valves were closed, as the headers shifted the pitch upward just enough to lessen the lower frequency that was the main cause of the boom.
3. PDK upshifts evoked a "snap" in the exhaust when driving moderate to aggressive, which I find exciting.
4. I felt a bit more torque in the middle rpm band, which is consistent with the dynamometer plots I have seen regarding the GMG headers.

My car is not tuned and I have never had a CEL from the headers. That said, I was still not fully satisfied, as the transition from closed to open values was too abrupt for me. My solution was to purchase a Cargraphic exhaust valve controller from a fellow on Rennlist. It allows the exhaust vales to be fully open at all rpms, but it reverts to the stock programming with a push of the button. So the above benefits remain and the abrupt valve transition has been eliminated at the push of a button. The option of GMG catted headers, GMG CMB, and OE side mufflers with the Cargraphic exhaust controller is the ticket for me. I have had many people compliment me on the sound of this set-up.

Since you have the OE side mufflers, another option for you would be to reinstall them and then purchase catted headers to go along with your Sharkwerks CMB. Let us know what you decide and your opinion on it. Good luck.

 

My vote is catted Dundon headers and stock center muffler. I find it perfect.

 

I had the full set up (with cats) from Dundon on my 991.1RS with no CEL issues (and no tune on my car). Loved the sound and boost in power.

 

Hey Sonder,

I also live in the DFW area. I've got a Soul CMB on my 991.1 GT3. My experience with the Soul center is that it is one of the louder CMB options. It is noticeably louder than cars I've heard with Sharkwerks and GMG centers. Quite a few folks have thought my car has a full system when in fact I still have stock side mufflers. I have been toying with the idea of also getting the Soul SMB but I'm afraid of the car no longer being drivable on the highway. I have zero issues with drone right now, and the car can cruise quite comfortably when the exhaust button is set to Off.

I'm happy to meet up. For exhausts, you really have to hear it in person to decide. I'm also very curious to hear your setup.

 

Thanks for the well wishes and the insights. I have a little apprehension about the Dundon street headers because I have no tolerance for CELs. The more people that can let me know they're not having issues, the better. I echo your sentiment on the Cargraphic valve controller; I already have that installed because the abrupt opening midway through the RPM range is nonsensical when you have aftermarket exhaust parts. I think I'll keep an eye on classifieds for those street headers and if the price is right, it's worth a try. Nothing that can't be undone.

My reservation on the stock center is that it could crack and not have a warranty. Last night, I ordered the Dundon loud muffler and plan to try this with my valved Soul SMD. If I want more at that point, headers could put it in the best spot. I just need to hear how loud the Dundon loud center muffler is with no side pipes.

Thank you. Power is always nice but the car is plenty fast. I'll see if I can find them used for cheap to try out.

There is no chance you'll like having both Soul muffler deletes, but I'll PM you and I'd like to meet up.

Edit: looks like I can't PM you, @Xec. If you're able to PM me, please share your contact info. I don't have an Instagram account, but I'll have someone shoot you a dm if I can.

 

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Brief update: I ordered a loud Dundon muffler on Aug. 5th after talking with Jamie about my needs a bit. I'll post another update when I have thoughts about the Soul valved side delete + loud Dundon center.

In the interim: the Sharkwerks CMD with the OEM sides I used to run is definitely a bit quieter than the Soul CMD that I heard on @Xec's car. I probably would still have pursued this option instead of swapping CMDs because of the weight savings and reduced rear tire temperatures, but it likely would have been enough noise if that were the only factor in consideration.

 

I may be selling an Akrapovic slip on off my 2019 gt3 touring that is being delivered tomorrow. Haven't driven the car yet so depending on whether I like it or not. Located in Los Angeles. If you are interested send me a private message.

 

Do you have a white GT3? Saw one on Northwest Highway by Kellers on Wednesday.

 

I'm in the DFW area. Like Sterling and Bogey recommend, I have the Dundon street headers and cats but kept the OEM center muffler. Sounds perfect to me, virtually no drone, exotically loud but not TOO loud (exhaust valves do help somewhat at idle), and the sound is just intoxicating. To me, just doing a CMD or side muffler removal gives you the volume, but doesn't give you the "beef" of a performance exhaust. To me, it just sounds more hollow and boomy, whereas headers give you that muscle sound as well. Since I don't track, I don't foresee any issues with the OEM center muffler cracking under extended high heat. The extra power is slight, but noticeable.

Downsides: 1) Dundon LOVE their exhausts and it's hard to pry them away! 2) I did have ​​a CEL from a POST-cat O2 sensor. One of my hi-flow cats (driver's side) wasn't doing the job. However, this can be solved for a few more bucks and some creative engineering and no tune was needed.

I'm around if you want to hear my setup, although it sounds like you've already sampled Dundon.

 

I appreciate the thought, but the Dundon muffler has sold me (details below).

Wasn't me. I haven't been on that road.


@Limey Hooligan I'd definitely like to hear your setup. I'm interested in what you did to solve the issue with the cat.

Now, an update. I ran with no side or center mufflers for the last month or so, including a weekend at Circuit of the Americas. The drone is too much for daily driving (95 MPH is around 4K RPM and there is a NASTY drone at this point in the rev band), though the sound is amazing. I'd wager the car would sound most like a race car with the Dundon headers and a center delete, but I'm not going to find out. I won't be returning to a no-muffler configuration. Driving on track, the sound is right at home, but ear plugs are recommended. Even just Armco barriers being next to you fills your head with the noise. If you don't have ear plugs, your ears will be ringing at the end of the day.

Today, I got the Dundon loud center muffler installed with the valved Soul side muffler delete (OEM headers). Once again, the car is completely acceptable as a daily driver in this configuration. Exhaust drones are completely gone with the valves closed and, even if you open them, it's not so much of a drone as it is just good noise. My only complaint is that, at least compared to no mufflers at all, it's too quiet for my taste, though it's obviously louder than OEM. I think it's probably just a bit louder than the center delete only, but I found the CMD with OEM sides too quiet and that's what sent me down the rabbit hole in the first place.

I won't re-install the side mufflers, nor will I go without a center muffler. That just leaves me with the Dundon headers, which to their point was their original recommendation (which was to buy the whole system, but what vendor doesn't recommend selling more of their stuff?). The problem with going that route is that I have to consider replacing the newly-installed Dundon center muffler because of the difference in diameter (Dundon headers can come in both 3" and 2.5" variants, and the Dundon loud muffler I purchased is in the 2.5" configuration to fit the Soul valved SMD). I could purchase the headers in the 2.5" configuration and leave the muffler alone, but I'd wonder if it were done right, and I'd wonder about the difference in sound and power. I'd probably have a hard time putting it out of my head.

If I did it all again, having the knowledge and experience I do now, I'd just get the full Dundon setup in the 3" configuration (provided I had a money-back guarantee that I would get no check engine light). I'll drive another week or so like this and see what makes the most sense.

 

Yes, Dundon street headers for the win!
Just keep your 2.5" Dundon center muffler and get the headers, cats, and 2.5" valved pipes to match. Unless you also install the Dundon intake kit and larger throttle body, you're going to see negligible power increase just going from a 2.5" to a 3" exhaust - verified with Jamie at Dundon. So, keep the Dundon center muffler and get the rest of their exhaust to match.

I'll PM you my cell phone so we can meet up.