SL/R231: How to quiet an SL400
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Toyota Prius V
How to quiet an SL400
I'm considering buying an R231, and have driven a couple pre-facelift cars (SL550 & SL400). I am leaning toward an SL400. The only misgiving I have with it is they seem a bit louder. I like the quiet of the SL550. I understand there is a sound generator in the trunk of many/most/all SL400s that seems easy to disable, but have also read that it doesn't do much after startup. I'm wondering if SL550 mufflers are a direct swap into the SL400. Looking at the MB parts catalog, it lists different part numbers, but also says that some mufflers for 8 cylinder cars will fit 6 cylinder cars, although without details (and why there are 2 part numbers listed for some situations, like right rear muffler for 8 cylinder cars, at significantly different prices). Or is there some other way to quiet the car, or if it's not just the exhaust system, but the engine is fundamentally noisier. Really, any info to help guide this decision. Thank you for any info you can provide.
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What type of tires on the SL400’s you have been driving? Where any exhaust or engine modifications done to them? I have driven a few R231’s and only felt the AMG’s are loud. Even the V8 unless you are way up in the RPM’s isn’t really that loud.
Last edited by C280 Sport; Mar 7, 2026 at 08:28 PM.
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Toyota Prius V
Good questions. The cars were at dealers, and it didn't occur to me to look underneath, and I also don't know what kind of tires were installed. These are definitely things I will look at on future cars. None of the cars were terribly loud, not aftermarket loud, but they weren't luxury car quiet, like the SL550s were. I have driven 3 SL400s, one of the dealers said he understood about the sound, that the SL550s were quieter, which surprised me, but was the first indication that this is something I should look into. I have no way of knowing if they had anything removed, though, at this point. There si one for sale from a private party about 1.5 hours from me, and I'm trying to figure out what my approach will be if I otherwise like the car, but it is louder than I'd like.
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From: Newbury Park, CA
2016 SL400 & 2021 C300
I do not find my SL400 to be particularly loud, but my hearing is poor and when I wear my hearing aids it is noticeably louder. Mostly I hear engine sounds and wind more so than the exhaust. When I put Michelin sport tires on my car I noticed much more road noise than before. I wanted a different tire, Continental Contacts?, but they were unavailable at the time so I settled for the Michelins. For me, tire noise is a bigger problem than exhaust sounds but then again, I would be fine with a louder exhaust. My previous car was a Vette with super sport exhaust that was wired with a mild to wild setting for increasing the volume. As it is, sport mode seems to increase the volume a bit and really increases performance and driving fun.
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2019 SL450, 2019 E450 Luxury Trim Wagon, 2024 BMW I7 xDrive60
My SL450 has what I feel is a bit too loud of an exhaust note, when I depress the accelerator pedal a bit more than I usually do, especially to the point where it downshifts. This is one of my only issues with the car and find it to be amazingly quiet otherwise, for this type of vehicle. I believe—but do not know for sure—that there is an exhaust “flap” that opens up on stronger acceleration. Is there someone here who can confirm this? Perhaps our friend Carconsulting might be able to shed some light on this subject?
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My SL450 has what I feel is a bit too loud of an exhaust note, when I depress the accelerator pedal a bit more than I usually do, especially to the point where it downshifts. This is one of my only issues with the car and find it to be amazingly quiet otherwise, for this type of vehicle. I believe—but do not know for sure—that there is an exhaust “flap” that opens up on stronger acceleration. Is there someone here who can confirm this? Perhaps our friend Carconsulting might be able to shed some light on this subject?
in all of my BMWs, I was able to adjust the exhaust the flap positioning via the setting menu or coding
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From: Corona Del Mar, CA
2019 SL450, 2019 E450 Luxury Trim Wagon, 2024 BMW I7 xDrive60
I’d check with @EleBest if this can be controlled via software coding.
in all of my BMWs, I was able to adjust the exhaust the flap positioning via the setting menu or coding
in all of my BMWs, I was able to adjust the exhaust the flap positioning via the setting menu or coding
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MBWorld Fanatic!
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From: Corona Del Mar, CA
2019 SL450, 2019 E450 Luxury Trim Wagon, 2024 BMW I7 xDrive60
I’d check with @EleBest if this can be controlled via software coding.
in all of my BMWs, I was able to adjust the exhaust the flap positioning via the setting menu or coding
in all of my BMWs, I was able to adjust the exhaust the flap positioning via the setting menu or coding
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Toyota Prius V
The car is now at a used car lot. I went to look at it. It was quieter than I remember the other SL400s I drove. At idle it sounded like mothing unusual, but on hard acceleration, it made a nice throaty roar. At part throttle on the highway, it got a bit loud, but not as sonorous as at full throttle. I checked underneath (as best I could these cars are LOW), and it looked all stock. I checked in the trunk, under the trunk floor, and there was no exhaust sound generator. Now the tough part -the buy or not buy decision.
