Another muffler exhaust question.

[Dontilgon]

I enjoy the sound of my stock exhaust but would like to update the design or clean up the engine compartment. Clearly all the newer aftermarket systems out there do this very nicely. The only problem I find with this new systems are they are bit noisy or drone. Does anyone have experience with an aftermarket quiet exhaust. Honestly if there was replacement headers that mounted to the stock exhaust , that would be the perfect solution for me. I have a test pipe and this was all the extra sound I enjoy. Also what is the deal with the wrap around exhaust design, seems a bit complex for an exhaust system. Thanks in advance

[opethmike]

Yes.

[Josh]

If you want quiet, stick with the stock exhaust.

[Dontilgon]

If you want quiet, stick with the stock exhaust.
yep, I saw that coming . Was just checking if someone out there had a aftermarket exhaust system that was close to stock.

[jangell]

Yeah, it seems that the aftermarket version of "quiet" is a lot different than what people who actually want a quiet exhaust think it is. I have an almost-finished 3.0L conversion with DPI headers running through Magnaflow CARB-compliant cats and into a dual in/dual out Borla Pro XS muffler. The Borla is supposedly "quiet", but that seems to be relative to all the other free-flow aftermarket mufflers. It still seems pretty loud to me.

Now, so far I've only run it in a garage, which is making it extra loud. Once I'm back on the road, I'm going to take measurements outside at 50 and 100 feet using a sound meter. About a month after that I'll be installing two three-disc Car Chemistry silencers in the pipes between the cats and the mufflers with stainless steel wool packed between them and measuring the sound again. In theory they'll cut 3-10 dB of noise out (where every 10 db is approximately halving the sound level). However, this will reduce the performance. Which I'm fine with, because I'll sacrifice power for quiet. I have a second set of inserts I want to install after the muffler as well; these will be less effective, but I want to see what they do to the noise level.

Also, the crossover inside the muffler should reduce droning (like what x-pipes do, or so I'm led to believe by Google). I originally had a grand plan to install two cats, then have the pipes go up at a 45 degree angle, though some resonators, into an X-pupe, then down to separate mufflers before exiting out the tailpipes. There is nowhere near enough room for that. My next idea was to run the pipes forward under the transaxles and out the sides, but there's no room for that under the car, and it would just be silly anyway. :)

I'll report back when I've actually done the sound tests. If all goes well, I'll be driving the car this or next weekend, assuming no unexpected issues crop up (it's been about 5 years, so this wouldn't surprise me, but I'm hopeful everything will go well).

-- Joe

[FABombjoy]

The stock crossover contributes to the quietness of the system, as does the stock pipe diameter and cork.. er "muffler".

Rear engine means short path for tubing which makes it a challenge to bring out the pleasing lower-tones. Consider the tonal differences between a trumpet and a tuba: both have the same mouthpiece but the tuba has 2-3x more tubing length.

This is the OEM system from a Carrera. Gargantuan mufflers, twin cats, and a fair amount of pipe:
https://cdn4.pelicanparts.com/techarticles/Porsche-996-997-Carrera/47-EXHAUST-High_Performance_Exhaust/images_small/pic01.jpg

Compare to the king of shortness:
https://www.deloreanautoparts.com/delorean-parts/images/header-kit-2.jpg

With a crossover muffler design like DPI or DMCH at least you get a larger muffler body and additional pipe length. You can try to kill drone with resonators or cats or other such devices but I haven't seen much success with that strategy. The muffler should be doing the heavy lifting.

Philosophically I feel very strongly that best muffler is a turbocharger :D

[louielouie2000]

Someone asked this exact question last year. Josh at DPI offered to cut open one of his Spec I mufflers to see if any additional stainless steel wool packing material could be added. I'm not sure if the owner actually had Josh do that, though. There are also debates regarding the merits of muffler packing materials, be it steel wool or fiberglass. I believe fiberglass is quieter, but won't hold up to high temps as well. Which I suspect is definitely an issue with the aftermarket DeLorean systems, seeing how the headers, cats, and mufflers all feed immediately into each other with no chance of heat dissipation.

I know this is going to be Teitelbaum obvious, but retaining the catalytic converters on any of the aftermarket kits definitely helps cut down on the noise vs replacing them with "test pipes." Regardless, all the aftermarket systems are louder than stock. I believe the modern DMC-Texas systems are probably the quietest of the aftermarket lot, though.

[jangell]

I'm impressed by how convoluted that Carerra exhaust is.

You could probably do the dual-mufflers routed past each other, but you'd need a way to bend the pipes to pull it off, and that's out of the scope of most DIY people (I stuck with pre-bent pipes and slip joints, mostly). Maybe you could use a series of 45 and 90 degree pre-bent pipes, but you'd either have to weld them or leave a lot of space for clamps. An even then, it might just BARELY fit, car-width-wise. I doubt you could also fit resonators under the mufflers. That would be more ideal but probably too tight.

My Borla Pro XS install is really not much different from the DPI or DMC setup, but less elegant (they have nicely bent pipes), configuration-wise. It was more a learning exercise and allowed me to experiment more easily, and I can swap out individual parts to try out different configurations if I want, especially since everything is only clamped together. I also used 2.5" pipe; using smaller pipe would have reduced noise as well, as will the silencers that I plan to put in (they're basically corks).

-- Joe

[jangell]

Someone asked this exact question last year. Josh at DPI offered to cut open one of his Spec I mufflers to see if any additional stainless steel wool packing material could be added. I'm not sure if the owner actually had Josh do that, though.

I am said owner. I sent the exhaust to DPI at the end of July 2015 (everything but the headers). I heard back in December 2015 that it was ready to test, and they wanted to match it to an engine similar to what I had (3.0L) to see how it sounded. In November 2016 I got an email saying that it was ready to ship, and they just needed to know where to send it. I sent the info, but I never heard back. I sent a few more emails and left some voicemails, but by the middle of 2017 I just gave up and built my own exhaust using the DPI headers as a base. I'm not out any money or anything (just time), and I wasn't going to use the DPI muffler anymore if it wasn't silenced anyway, so it's not a huge loss to me.

Point is, I don't know if the silenced SPEC I works or not. :)

-- Joe

[Delorean Industries]

Joe, I was unaware we didn't send you a test muffler back. This fell through the cracks apparently. Let us know what we can do to make it right even though you made your own.

[jangell]

Thanks. I guess you can send me the muffler back. :) If you still have it around, that is. I'm kind of curious how it compares to the one I built, sound-wise. Due to the limitations of using pre-bent pipes, mine isn't exactly perfectly lined up either (tilted a little, one tail pipe is a little long, and it hangs a little low, but it gets the job done).

-- Joe

[jangell]

Now that my car is finally on the road again, I did a crude test on how loud my exhaust is. I used a simple dB meter I got off of Amazon a while back, and was only standing about 15-20 feet behind the car while it was idling (already warmed up), pointing the meter right at the back of the car. I got just under 85 dB. Not bad. When standing in front of the car it's surprisingly quiet. I need to do something with more standard meter placement and distance at some point, once I figure out what that is...

As mentioned before, the setup is DPI headers, off-the-shelf CARB-compliant cats, 2.5" pipes, and a Borla Pro XS dual in/dual out muffler. Unlike normal DMC mufflers, the Borla is designed with both inlets on one side and both outlets on the other side (although it's reversible, so it doesn't matter which side is which), so I can't just plug the inlets into the "top" and the outlets into the "bottom". To work around this, I have drivers side going in and out of the "top" of the muffler, while the passenger side goes through the "bottom". It sits low for a DeLorean muffler due to the pre-bent pipes and clamps. I'm also using heat shield wrap instead of a metal shield to keep the heat off the engine, just for simplicity.

I did find what I'll describe as a "buzz" from the exhaust at >2000 RPM. This was just the right frequency to be annoying. To counter this, I installed two Car Chemistry three disc silencers in the pipes after the muffler, one on each side. I had welded the cap-with-a-hole on the muffler side of the silencers to bring it down a little bit. This mostly removed the buzz and made the car much more enjoyable to drive. I think it also dropped a few decibels -- not a lot, but it sounds quieter to me. I of course didn't think to do before-and-after sounds tests, so all I have is the after reading of 85 dB. At some point I'll probably drop the exhaust and install two other pipes between the cats and muffler that include two more CC inserts that have both caps welded on and stainless steel wool between the rings, which would probably lower the noise a few more decibels, but I'm not in a hurry to do that just yet.

Overall, the sound is fine to me. It's not terribly low, but it's not very high either. It's not exactly quiet, but it's not super loud either -- it's diesel truck levels, or around what my wife's '72 Charge puts out (although that has a lower note than my exhaust setup). I don't remember what the stock or DPI exhausts sound like at this point, so I can't really compare them, and video always sounds different than real life, but I'll try to capture one this weekend.

-- Joe

[jangell]

Some quick Googling found this document (https://www.ntc.gov.au/Media/Reports/(9745A524-E60D-9B7C-835B-CDAF7DC19D8B).pdf) (it's for Australia, but other things I found seem to match), which suggests the meter be positioned about 1.64' (0.5m) way from the exhaust on a 45 degree angle (there's a diagram in the document), and revved at 3000 RPM. It also notes to make sure that there aren't any noise reflections by mounting the meter on a tripod, although I'll probably just stand to the side and hold it at arm's length. :)

I'll try to get a measurement done this weekend, along with a video of the exhaust noise and note.

-- Joe

[jangell]

So doing that test at 790 RPM warmed up yielded ~96 dBc. Not exactly what I’d call quiet. Maybe I will install that second set of silencers...

Although apparently a lot of regulatory sound tests are done with the dBa filter, to dBc. Maybe I’ll hunt down one of those meters and try again.

— Joe

[vwdmc16]

Any scientific test been done to measure the Db of stock exhaust?

[hippieman9]

I enjoy the sound of my stock exhaust but would like to update the design or clean up the engine compartment. Clearly all the newer aftermarket systems out there do this very nicely. The only problem I find with this new systems are they are bit noisy or drone. Does anyone have experience with an aftermarket quiet exhaust. Honestly if there was replacement headers that mounted to the stock exhaust , that would be the perfect solution for me. I have a test pipe and this was all the extra sound I enjoy. Also what is the deal with the wrap around exhaust design, seems a bit complex for an exhaust system. Thanks in advance

I was concerned with drone noise in my car too. hesitant on what exhaust to buy. I ended up with DPIs Spec 1 and I love it. It doesn't seem to drone much at all, I can listen to the radio (craig) no issues. The headers go down and back so most heat is away from engine compartment. (getting rid of the cross over pipe was a huge improvement) little more performance is gained, and slightly more aggressive sound. all around a great exhaust and Josh stands by it too. ( I do however highly recommend replacing the bundle of brown wires from the alternator to the starter with a heavy battery cable, and securing it away from the headers.)

[dmcnc]

I was concerned with drone noise in my car too. hesitant on what exhaust to buy. I ended up with DPIs Spec 1 and I love it. It doesn't seem to drone much at all, I can listen to the radio (craig) no issues. The headers go down and back so most heat is away from engine compartment. (getting rid of the cross over pipe was a huge improvement) little more performance is gained, and slightly more aggressive sound. all around a great exhaust and Josh stands by it too. ( I do however highly recommend replacing the bundle of brown wires from the alternator to the starter with a heavy battery cable, and securing it away from the headers.)

I can vouch to this. I also changed mine for a SPEC 1 and the drone is significantly lower: a huge plus for me as a daily driver.

[jangell]

I did another test with a nice new dBa meter, and got 76 dBa at warm idle. This was standing about a foot and a half away at a 45 degree angle from the exhaust with the meter pointed at the exhaust.

Also, I think I have an exhaust leak that seals itself when the car gets warm. Today was a medium-length highway trip, and when I got home the car was noticeably quieter than when I left. I'll be taking apart the exhaust in a couple of weeks and adding some sealer between the clamps to see if I can get it to be quiet (76 dBa) all the time at idle. I'll try to do some 3000 RPM tests after that's taken care of.

Also, the grade of stainless steel for my exhaust may not be the best. The Borla Pro XS muffler seems fine, as do the DPI headers, but the stainless steel Walker catalytic converter already has a fair bit of surface rust on it, as do some of the pipes. The apparently steel hardware on the stainless steel clamps is also rusty and starting to corrode. The one piece I expected rust on, the steel ends that I welded the flange onto to mate to the exhaust headers, does indeed have obvious rust. Admittedly, I'm driving the car in winter (not much snow this year, but they still salt the roads), and completed two 2.5 hours highway trips a couple of weeks ago, but that still seems a bit fast -- the car has been on the road for under a month and a half.

-- Joe

59226

[Farrar]

Joe, your exhaust interests me because I also have a 3.0L, but I have two Borla Pro XS mufflers rather than one dual. Near 2,500 RPM or so I have a pretty bad drone - one note that permeates quite strongly. But I haven't been able to document just how loud it is.

[jangell]

The Car Chemistry inserts might help with the drone. It seemed to help with mine, which was at about the same RPMs. JEGS has them (https://www.jegs.com/p/Car-Chemistry/Car-Chemistry-Collector-Inserts/744688/10002/-1) for $57 each for the 2.5" with 3 discs (more discs means more silencing). You'll likely want a bench grinder handy so you can sand off the paint around the edges of the discs and a bit of the metal so that they'll actually fit in your pipes. You then rivet them in place (I used a magnet to find the discs), or run a bolt or wire through the pipe so they don't shoot out the back. While the CC guys say to install them before the mufflers but after the cats, you can install them after the mufflers as well. They just work best with hotter engine gases, but our exhaust is so short that there really isn't much of a run for them to cool down.

I've attached some more pictures of my exhaust. As I mentioned before, the muffler hangs low so that the cats can run under the frame and body instead of being tucked inside of it closer to the engine, and to allow the use of pre-bent pipes. If you can bend the pipes, you can raise it up to more of a stock height. The pics sort of show the routing of the pipes, with the driver's side going through the "bottom" while the passenger side goes through the "top".

I also realized that the amount of rust might be due to getting my engine tuned. I had this idea that I didn't need to put as much gas in the engine while decelerating (<30 MAP), so I leaned that way out. This seemed to introduce popping sounds in the exhaust at highway speeds when slowing down, which is apparently what happens when fuel burns in the exhaust instead of the engine. I did about two hours of continuous highway driving like this. Couple that with other over-lean problems I had due to a timing issue that caused the pipes and cats to glow while trying to get the engine idling mid last year, and it may simply be that the excessive heat ruined the anti-rusting properties of the stainless steel components. I'm going to replace the clamp hardware when I seal the exhaust in a few weeks.

I've been wondering what would happen if I did set up the dual in/dual out muffler I'm using with the exhaust ports from the engine both going into the "top" and the tailpipes going into the "bottom". There is a 2" or so hole that connects the top and bottom chambers, so the exhaust should still leave the car. However, the exhaust ports from the engine would be firing exhaust basically directly at each other -- the hole to the bottom chamber would be a kind of side street that he gases can take. This would undoubtedly rob a fair bit of power from the engine, although I don't know if it would damage it or the rest of the exhaust system from the gasses having such an indirect exit. I imagine the car would run quieter, though. I just don't want to damage something finding out.

Also, a correction: I'm running Magnaflow stainless steel cats, not Walkers; I had Walkers, but replaced them because the Magnaflows were SLIGHTLY shorter and allowed the exhaust to fit just a little bit better.

Someday I'l get around to making a new bracket to level the exhaust out; it sits a bit low on the right at the moment.

-- Joe

From behind:
592415924259240

Pipe routing (drivers side first, then passenger side)
5924659243

Tailpipes
5924459245

[David T]

Your rusting can also be due to the fact that Chinese S/S is prone to rusting. Overheating good S/S will just warp it, not make it rust. Popping and glowing in the exhaust is not due to being over lean, you are putting too MUCH fuel into the exhaust and it is burning in it getting it too hot or exploding (popping). If the popping gets too much you can actually blow the pipes apart. That's why you have decel valves on the throttle plates, to allow more air to get in if you slam the plates shut at high revs. The additional air leans the mixture to prevent the popping.

[dn010]

Your rusting can also be due to the fact that Chinese S/S is prone to rusting. Overheating good S/S will just warp it, not make it rust.


My UK stainless exhaust system rusted over after many years, I also drove many of these years on salted roads in the winter so I'm not sure if that has anything to do with it. I was pissed my $$$$ exhaust system ended up looking like this so I contacted the company about it. The company assured me that it was built using 304 grade stainless and the appearance was 'normal' for it's age. They wouldn't budge on this determination and me being in the US, was unable to do anything further about it except buy a new exhaust system. As far as catalytic converters, I bought DPIs spec exhaust and wish I would have gotten it with the converters instead of straight pipes, I'm so tired of smelling like exhaust when I am done driving the D.

http://dmctalk.org/attachment.php?attachmentid=36261&d=1440110812

[jangell]

The popping was happening with an AFR in the 18:1 to 22:1 (possibly higher; the wideband O2 sensor only goes to 22:1) range, if I remember correctly. The sound wasn't terribly easy to hear, though.

I had also assumed that too much fuel would cause the exhaust to glow, but back when my valve timing was messed up in August or so the AFR readings were way up over the 22:1 range.

Basically, my assumption was that the gas wasn't burning in the engine due to all the extra air and was instead making it to the exhaust where it burned instead. However, I really have no idea what I'm talking about.


As for the stainless steel pipes, yeah, that makes sense. The very short pipe with the flange to the headers is steel and I expected that to rust, but the Magnaflow cats and the other pipes (made by Vibrant) are stainless. I have no idea where the metal came from. The muffler looks good, though, as do the tips and the clamps themselves. The clamp hardware is aluminized steel.

-- Joe

[jangell]

My UK stainless exhaust system rusted over after many years, I also drove may years on salted roads in the winter so I'm not sure if that has anything to do with it. I was pissed my $$$$ exhaust system ended up looking like this so I contacted the company about it. The company assured me that it was built using 304 grade stainless and the appearance was 'normal' for it's age. They wouldn't budge on this determination and me being in the US, was unable to do anything further about it except buy a new exhaust system. As far as catalytic converters, I bought DPIs spec exhaust and wish I would have gotten it with the converters instead of straight pipes, I'm so tired of smelling like exhaust when I am done driving the D.

My mechanic friend saw my exhaust and felt that even though it's rusted that it would last until "the next owner", and he knows I have no intention of selling it.

The other good news about my rust is that my exhaust isn't terribly expensive. There's under $200 in pipes, under $100 in clamps and $140 for the muffler. The cats were $125 each, but only because I decided to be all local code compliant and get 50-state CARB cats instead of the cheap ones. There's another $50 in misc parts here (hangers, flanges, etc), and $50 in tail pipes. The DPI headers cost as much as the entire rest of the exhaust, but those have to be built specifically for the 2.8L/3.0L engine, so that's to be expected. They also seem to be holding up very well, and I doubt I'll need to replace them anytime soon.

I'm not actually sure if the pipes and cats are 304 or 309 stainless (apparently 309 will show rust, but is still more resistant than steel); the JEGS and Summit Racing sites don't seem to say.

I should probably provide a link to my site where I discussion building the exhaust (and pictures of when it was nice and shiny): http://www.tmproductions.com/repairs-and-maintenance-blog/2017/8/26/building-an-exhaust. Note that I currently don't have the silencers in the pipes between the cats and muffler, as I took them out when diagnosing the glowing cats and pipes; instead, I have silencers without stainless steel wool packing in the pipes leading out of the muffler to the tailpipes

-- Joe

[Farrar]

The Car Chemistry inserts might help with the drone. It seemed to help with mine, which was at about the same RPMs. JEGS has them (https://www.jegs.com/p/Car-Chemistry/Car-Chemistry-Collector-Inserts/744688/10002/-1) for $57 each for the 2.5" with 3 discs (more discs means more silencing). You'll likely want a bench grinder handy so you can sand off the paint around the edges of the discs and a bit of the metal so that they'll actually fit in your pipes. You then rivet them in place (I used a magnet to find the discs), or run a bolt or wire through the pipe so they don't shoot out the back. While the CC guys say to install them before the mufflers but after the cats, you can install them after the mufflers as well. They just work best with hotter engine gases, but our exhaust is so short that there really isn't much of a run for them to cool down.

Thanks for that link! I guess in my case they would go ... in the tips? #2613's exhaust currently has tips made from 2-1/8" I.D. stainless steel tube, what I call the "McMaster-Carr specialty tips". ;) Before the engine swap I had resonator tips clamped on to the mufflers, but I installed them just before the 2.8L died so I never heard them. Bill just handed them back to me in a box. I don't think he even bothered with them. Or maybe he listened to them and decided they sounded awful. LOL My 2.25" in/out Borla exhaust is "throaty" and I do like the sound. It's not particularly loud, but it's not particularly quiet, either. (I made a video of it using my field recording kit for the best audio I could muster; it's on YouTube if you care to listen.) And of course I live in an area where there are no emissions requirements for antique vehicles.

Anyway, sorry for derailing this thread! But I am interested to see where you go next with your exhaust. :)

[David T]

On the subject of rusting stainless steel, I had a grill (made by a reputable manufacturer) and it rusted so much it turned brown. The story was they got a shipment of S/S and it turned out to be from Asia. It was supposed to be of good quality but it was not tested. It is a very insidious thing, having companies and countries counterfeit and misrepresent products. It can get purchased by other companies that expect and demand quality and when it turns out to be less than advertised, the products made from it suffer. Anyway Chinese S/S is not up to the standards it is expected to meet. The metallurgy is inferior and the properties of the metal do not conform to world standards. It doesn't matter what they say it is because it isn't. The quality control is non-existant. What do you expect, they make stuff out of the recycled garbage they buy from all over the world. About all you can say is that it is cheap. There is a good reason for that, it is junk.

[jangell]

Thanks for that link! I guess in my case they would go ... in the tips? #2613's exhaust currently has tips made from 2-1/8" I.D. stainless steel tube, what I call the "McMaster-Carr specialty tips". ;) Before the engine swap I had resonator tips clamped on to the mufflers, but I installed them just before the 2.8L died so I never heard them. Bill just handed them back to me in a box. I don't think he even bothered with them. Or maybe he listened to them and decided they sounded awful. LOL My 2.25" in/out Borla exhaust is "throaty" and I do like the sound. It's not particularly loud, but it's not particularly quiet, either. (I made a video of it using my field recording kit for the best audio I could muster; it's on YouTube if you care to listen.) And of course I live in an area where there are no emissions requirements for antique vehicles.

Anyway, sorry for derailing this thread! But I am interested to see where you go next with your exhaust. :)

I think I already derailed it by going into detail about my exhaust. :)

You can find some docs from Car Chemistry here (https://www.carchemistry.com/car-chemistry-inserts/). That includes installation instructions, which mostly boils down to which way they go in the pipes and what ends to optionally put the caps on.

You could put the inserts either before the muffler or in the tail pipes in your setup, assuming you have enough length to do so. It could extend into the muffler a little without being a problem, I imagine. You can cut off part of the long end if you need to, too.

This is one of the silencers stuck into the end of one of my pipes, with one of the caps (badly) welded on. I didn't grind off quite enough of the paint and edge metal on the discs, so I had to seat it with a rubber mallet and I still couldn't get it in as far as I would have liked, but it works fine.

59249

I don't know if this will help with your drone, but for $120 or so it's not too expensive to try, and shouldn't take long to install if your exhaust comes apart easily enough.

-- Joe