I know most of you guys consider the subject line to be an oxymoron -- but here's the deal: people ride in the back seat occasionally and when I put 4&quot; exhaust in I want them to be able to hear themselves think. <br><br>I've found a couple of options:<br><br>Diesel Dynamics makes a dual (straight through) muffler design which apparently is very near stock loudness. an extra $100 over their 4&quot; system. both mufflers are straight through, and no EGT increase has been measured. DD does their homework and I'm inclined to believe them on this.<br><br>Bullydog makes a baffled muffler claimed to be slightly softer than stock. They claim no increase in EGTs, even at 650 HP but (a) I've never been happy with the level of expertise on their technical customer service line, and (b) a baffled muffler is a restriction so I don't understand how they can claim this.<br><br>Both Bullydog and DD have bolt-on systems. Interestingly enough, DD recommends welding to minimize rattling and vibration. Bullydog claims the bolt on system works well. Has anyone tried either of these systems?

 

well, 4&quot; systems are usually loud, but i guess you've found some quiet ones. i have a gutted cat and a magnaflow flow-through muffler (stock downpie and tailpipe). i could barely hear a thing. i blocked out half of the muffler and it sounds like a typical 4&quot; system now.<br><br>Tom

 

The JRE system with a muffler is the quietest 4&quot; system I've heard yet. It's bearable straight piped ...

 

would it make any difference by relocating the muffler toward the rear the vehicle?

if you are worried about the EGT'S increasing by using a muffler, couldnt you just use a quiet muffler located toward the rear of the vehicle where it would be farthest from the heat from the turbo?

anyone tried it??

maybe it could be the new dodge cummins ricer look with the phat chrome tip at the end??

 

Magnaflow makes some short straight through mufflers that can be added into an existing 4&quot; system. Adding another muffler in front of the stock location with at least 6&quot; separating the two mufflers really calms things down.

 

I'm intrigued by the dual muffler approach. Especially the straight-throughs that DD is proposing. Whats interesting about their approach is that you put a small muffler close to the turbo (where the resonator is now) and a std muffler in the stock location. Theres some really cool acoustics theory going on there that I may have to read up on: these straight through mufflers seem more like acoustic absorbers to me. Which really is the objective -- you don't want to compromize the low backpressure of a 4&quot; system by putting a baffled muffler in there. You want to get the air out of the engine (present near zero backpressure) but dampen the acoustic energy contained in that same air. <br><br>Note that baffles are probably the most effective at reducing noise-- anytime you &quot;interrupt&quot; the air flow with anything, you create an opportunity to reflect sound waves back into the system and cancel out some of the noise. Its just that whenever you do that, you increase backpressure and compromise air flow.<br><br>as for reducing EGTs by moving the muffler -- I don't think that would work. EGTs are reduced by increasing air flow rate -- and a baffled muffler I think would restrict air flow in the same way no matter where it was placed. Its really the same principle as squeezing a garden hose -- squeeze it near the faucet or near the end, it doesn't matter as regards the total water flow through the hose.<br><br>understand that I don't have any direct experience in muffler and exhaust design, or even install experience, but I've never understood how moving the muffler towards the rear would influence anything other than in-cab noise. If you have a single baffled muffler, then I can see why -- you probably create sound wave reflections that tend to cancel each other out behind the muffler. I don't see that a straight through muffler would create the wave reflections that a baffled muffler would though. <br><br>anyone know of studies or experiments in this regard? Edward, your post seems to agree nicely with the DD approach. To me this is the most attractive approach because it addresses the acoustics problem without complicating the air flow problem.

 

The quietest out of the box 4&quot; system I've heard is the Magnaflow.They use a 3.5&quot; downpipe &amp; a 30&quot; body straight through muffler in the stock location.It sounds oem quiet to me under idle &amp; cruise conditions.At wot it's louder, but not substantially. I've built several dual muffler systems &amp; am a firm believer in a dual dampening system.Almost all, (maybe all) manufacturers use at least two dampening devices.Dodge used a convertor &amp; a muffler, &amp; now a resonator &amp; a muffler on the diesel applications.....

 

I have a bd 4&quot; resonator and muffler that just jumped out from under my truck and into the bed that i don't have any plans for.

 

[quote author=Doug link=board=7;threadid=7825;start=0#75469 date=1039014201]<br><br>Note that baffles are probably the most effective at reducing noise-- anytime you &quot;interrupt&quot; the air flow with anything, you create an opportunity to reflect sound waves back into the system and cancel out some of the noise. Its just that whenever you do that, you increase backpressure and compromise air flow.<br><br>as for reducing EGTs by moving the muffler -- I don't think that would work. EGTs are reduced by increasing air flow rate -- and a baffled muffler I think would restrict air flow in the same way no matter where it was placed. Its really the same principle as squeezing a garden hose -- squeeze it near the faucet or near the end, it doesn't matter as regards the total water flow through the hose.<br>[/quote]<br>DOUG-<br> ive been here for almost one week. it seems that your posts are coming straight from the text book or you really have a good grasp on knowledge and can 'splain yourself real good ;D <br> i can already tell you must be an engineer and have a very high IQ ! <br><br> let me 'splain myself a little more.<br><br> i was suggesting to put a quiet &quot;restrictive&quot; muffler at the end of the exhaust system farthest from the turbo.<br><br> the way i see it is that when the boost/fuel is up all the way and the EGT is coming up to max, the exhaust heat is most expansive closest to the turbo and cools off the further it goes down the exhaust stream.<br> so if any restrictive muffler that is placed closest to the turbo, it will be the most restrictive muffler too boot!<br> therefore a muffler being the farthest away from the turbo, should flow the same air because it has cooled off for 20 some feet <br><br> and the way i see your garden hose theory, if you sqeeze the hose nearest the faucet, you get a dribble at the end of the hose, and you sqeeze it toward the end of the hose, you get to wash your truck <br><br> let me know your thoughts-<br> if there was anyone to figure this out, i think it would be you.<br><br> take care<br>BRYAN<br><br> <br>

 

If you want real quiet like stock. Go with a Jardine and install a resonator in front of the muffler. Jardine uses Magnaflow mufflers.<br><br>This is the setup I have and it is quiet as stock.<br><br>Disclaimer: not affliated with Jardine.<br><br>Charles

 

heh heh heh. I wish I had a textbook on exhaust noise, but I'll have to really disclaim the IQ comment! I do like to think things through and have a good theoretical interest in all things cummins, but I'm just as average as the next guy. takes me a while to compose a post like this too ;D<br><br>There are really two problems here:<br><br>1. scavenging the hot exhaust gasses from the cylinders to reduce ETGs. This is really the simplest problem to understand, as there is really nothing magic and no rocket science going on -- just plain 'ol volume airflow. Air molecules per minute, if you will, and the more the better. This is a simple matter of flowing air from a high pressure point (the engine) to a low pressure point (the tailpipe). Air flows out the tailpipe because the exhaust manifold is a higher pressure than the tailpipe -- air moves in response to the pressure differential (sounds fancy but its really simple). The important thing to remember here is that air flow in a pipe is the same as water flow in a hose: it doesn't matter where you restrict the flow, the volume (cubic feet per minute) at any point in the pipe is the same. So for the purposes of ETG control it doesn't matter where you put the muffler(s) or resonator(s). Using the garden hose analogy, if you pinch the hose at the faucet, you will get, say, 1 gallon per minute out the end of the hose in a dribble. If you pinch the hose at the end, you still get 1 gallon per minute out the end, but it is a spray. The difference is where the &quot;spray&quot; occurs (inside the hose or at the end), but the volume of water is still the same. My point is that the &quot;spray pattern&quot; of the air in the pipe is a don't care as regards EGTs. it can dribble out the end or spray out the end -- either way, the volume is still the same and the EGTs are unaffected by the method. <br><br>What happens with a baffled muffler is that the velocity of the air molecules exiting the muffler is higher because of the restriction -- just the same as the velocity of water in a pinched hose is higher because of a restriction. So all you're doing by moving the muffler is changing the physical location in the pipe where the air changes velocity. If you put the muffler near the turbo, then the higher velocity air coming out the muffler will have to travel the rest of the pipe. It will swirl around more before settling down to a &quot;normal&quot; velocity. If you put the muffler at the tip, the air &quot;sprays&quot; outside the truck and the &quot;swirls&quot; occur in open air, just like spraying water on your truck. All this will do nothing for EGT control, but it will probably have an affect on noise. <br><br>now then, having said all of that: I think you may be right that a restrictive muffler near the turbo is more restrictive than if it were placed near the (cooler) end of the pipe. Yes, hot air is &quot;more expansive&quot; -- hot air near the engine certainly consumes more volume for its mass (it is less dense) and so its velocity must then be higher. That means for a given amount of air exiting the tailpipe, the air molecules striking the muffler do so at a higher speed and therefore bounce around more and experience more restriction. putting the muffler at the cooler end of the pipe means that the air is more dense -- so air molecules hit the muffler at a slower speed. <br><br>The number of air molecules per second that have to exit the engine (to maintain EGT) remains the same -- they (the air molecules) just take up more space near the engine than they do after cooling -- but they all have to go through the same pipe, they all hit the muffler no matter where is it placed. But you are right that that hotter air moves faster (because it takes up more space) and so the muffler near the turbo is more restricitive because the air molecules hit faster and bounce around more.<br><br>2. taming the acoustics problem of external noise. This one is harder to understand because of the vast complexity of sound. you have essentially three things going on: (a) air noise due to velocity -- when the wind blows harder you here swishing noises. (b) pulsing sound waves generated by the engine. like waves on a moving river, sound waves travel in the pipe independant of the speed at which the air itself may be moving. (c) mechanical resonances (howling) of the parts. <br><br>higher velocity gasses will probably result in louder noise and may induce more mechanical resonances -- hence my prediction that a muffler close to the turbo will sound louder than one near the tip, as well as be more restrictive. I only say that because, once the air leaves the muffler, it is traveling faster than it did when it entered the muffler (just like water travels faster after the pinched hose restriction than it did when it entered the restriction). Also, as I mentioned before, a muffler at the tip also allows the potential for a sound wave to reflect back into the pipe and do some canceling. Thats the magic -- a sound wave coming down the pipe can hit a restriction and start traveling back up towards the engine. ever see a wave on a river travel up stream against the flow? same principle. unless the exhaust gasses travel down the pipe faster than the speed of sound (which would be very exciting indeed) then sound waves can travel both up and down the pipe. <br><br>pipe diameter, corner radius, and bending methods affect wind noise (&quot;a&quot; above&quot as does any restriction such as a baffled muffler. This isn't much of a problem.<br><br>resonators and mufflers deal with sound waves (&quot;b&quot; above&quot. Their design and placement will interact with all the other factors as well (air velocity noise and mechanical resonances), such that the complete design (for lowest noise) is pretty hard to predict from your armchair (read, lots of engineering effort...). <br><br>the mechanical geometries, materials, connections, welds, etc. of the exhaust components govern the potential for resonances (&quot;c&quot; above). In other words, the pipe can actually howl in response to air moving through it -- and the note(s) that is resonates at will be almost impossible to predict without experimentation. <br><br>As I mentioned before, the beauty of the straight-through mufflers is that you can separate the two main problems (air flow and acoustics). That is, they (the straight through mufflers) have little, if any, affect on air flow. So you can play with placement and optimize your acoustic goals without messing up the air flow piece. On the other hand, once you have a restrictive muffler, then suddenly the noise problem and the air flow (EGT) problem are hightly inter-related.<br><br>there's something about the dual, straight-through muffler design that appears to have some acoustic cleverness, if you will. There is potential to create sound wave cancellation without restricting air flow (that is waves traveling up stream without affecting the downstream flow rate). You see, if you suddenly increase the diameter of the pipe, you also create the opportunity for a sound wave reflection. thats cool. These straight-through mufflers (some of them) have mesh materials in them but still preserve the 4&quot; diameter properties of air flow and present a &quot;suddenly increasing&quot; diameter. I just wonder about the potential magic that may happen with two of those in the same pipe.<br><br>ok thats enough verbiage for now -- Doug<br><br><br>

 

;D<br> DOUG-<br><br> now we are getting somewhere with this-<br>i dont want to stray to far from the subject, but i know these trucks have a certain drone to them- <br>in my 87 BUICK TURBO REGAL it has this certain drone we call the 2200 RPM drone-<br> all 3.8 turbo cars drone (yes i know they arent diesels) but someone came up with this great idea and solved the persistant drone issue!!!<br><br> they installed these reducer bells that, as you said &quot;for sound wave reflection&quot; that reduce the noise level-<br> since our exhaust systems are usually 3&quot; downpipe to the 2 1/2 duals out the back- some guys are installing the bells after the mufflers with good results they are about 2 inches long, and instead of increasing the size of the pipe, they reduce it- the easiest way for me to explain it is it looks like a &quot;bell&quot;- kinda if you were to take a 1/2 inch pipe down to 3/8 pipe, the fitting would be the same shape as these pieces im talking about- <br> <br> ive always heard that when air gets pushed around a airplanes wing, the air speeds up from the shape of the wing-<br> kinda like what this guy is selling on ebay *i dont know the company or if it works or not*<br><br>http://cgi.ebay.com/ebaymotors/ws/eB...tem=1874011267<br><br> anyway, back on the air moving around corners and changing the sound of the engine-<br><br> back when i was in highschool, we would mess around with air intake systems (back before ricers had fart cannon style mufflers) to change the sound of the engine under a load-<br><br> this got me thinking a few months ago-<br> what if i applied the same technique on my truck, so i went out and looked under the hood and found the drivers side intercooler pipe- its about 2 ?? 2 1/2 feet long, and straight 3 inch piece of pipe-- <br>if that pipe was flared out like the muffler selling on ebay * look at the picture * it may/may not change the harmonics in the engine, but it would definitely speed the air up going into the engine- ;D<br> years ago this 60 year old good ole boy at my work went on and on about how PROCHARGER (guys who make superchargers for all makes and models) was using that style of pipe right before the throttle body- and i asked him what the heck he was talking about ??? ??? its just a piece of pipe right?<br> <br> turns out this guy RICHARD MILLER is a genious and had his hands in the project and gave them tips on how to &quot;improve&quot; the boost pressure--<br>smaller pulley=belt slip so they had to think of something-<br> yup thats right-- ole D!CK MILLER got them an honest increase of boost just with the pipe trick-<br><br>what does this have to do with mufflers/noise/EGT/ect,ect,ect??<br><br> perhaps we need some more testing <br><br>

 

Have you ever heard a CTD Dodge with a Banks exhaust on it? Its pretty quiet IMO. Quiet performance exhausts are lame IMO. But, To Each Their Own, I guess. PLEASE NOTE: I am in NO WAY affiliated with the aforementioned company. I was just offering a suggestion.

 

I'm with Doug, the quiter, the better. In fact, straight piped trucks are not only loud, but sound down right crappy IMO. I'll never understand why someone would want their exhaust louder, but can garantee those feelings will change with age.

 

[quote author=patriot pearl blue link=board=7;threadid=7825;start=0#76232 date=1039133565]<br>they installed these reducer bells that, as you said &quot;for sound wave reflection&quot; that reduce the noise level-<br>[/quote]<br><br>There's two things going on here, but before I get into that, note that exhaust scavenging in a Buick 3.8L (I had one of those in a 1982 Century) doesn't carry the same flow requirements as our diesels do. That is, this engine can probably tolerate some minor additional restrictions in the exhaust system -- hence the effectiveness of the bell restriction with apparently no negative impact.<br><br>Anyway, what I suspect is going on here is a combination of two things: (1) reflection of sound waves in the exhaust air, back towards the engine and (2) breakup of mechanical resonances in the pipe itself. As regards the &quot;drone&quot; as we usually refer to it here, I suspect that latter (mechanical resonances) is probably dominant over the former (sound wave reflection). But certainly they could both be a factor. The thing about a drone is that it is a resonance -- something vibrating at a certain frequency (or narrow bandwidth of frequencies) in response to the exhaust air movement. So the reducing bell things eliminate drones (I believe) mostly because they break up the exhaust pipe into mechanical sections -- essentially raising their natural resonance properties to a audio region that we dont' care about. In that sense, placement of these bell reducers is probably not critical -- the goal is to eliminate one long pipe in favor of two or more sections. one long pipe will drone, while the shorter sections won't. <br><br>The thing about sound wave reflections back towards the engine is that they are nearly impossible to predict without extensive modeling and mathematics work. I did a quick approximation and discovered that the opportunity you have of eliminating &quot;drone&quot; coming from the exhaust air itself (not the pipe resonating) would be in the ~400 Hz and above region. To give you an Idea of how high or low 400 Hz is, consider the tones in a woman's speaking voice or (if you are musically inclined) the note &quot;A&quot; above &quot;middle C&quot; on the piano. <br><br>This is all pretty subjective, too. for example, I'm not saying that the pipe itself cannot &quot;drone&quot; at 400 Hz. That is certainly possible. I'm only saying that using a bell reducer or other restriction (including a muffler) to reflect sound waves back towards the engine in hopes of gaining cancellation effect in the exhaust gasses themselves, will be effective only for drones of this nature.<br><br><br>My guess is that the restriction, from an air volume perspective, is not critical here, and that the bells are breaking up pipe resonances, not air resonances. In other words, the pipe section after the muffler may be resonating. The side effect of increased backpressure (due to the restriction) is apparently inconsequential.<br><br>yes, the airfoil shape of the wing forces the air velocity above the wing to be greater than the air velocity below the wing -- becaue it has to travel a greater distance. The faster air, compared to the slower air, creates a lower pressure above the wing and therefore a force pushes up on the airplane wing. <br><br>But remember that creating such an air pressure differential, and the &quot;magic&quot; that results, requires energy. you don't get something for nothing. my point is that something has to force the air above wing to go faster (it just doesn't move by itself), and that energy has to come from the fuel burning in the airplane's engine. that is (in part) how forward thrust gets converted to upward force. remember that principle when thinking about the following...<br><br>There's so much room for snake oil techno-babble in this guy's product discription that I remain convinced only of his desire to make a quick buck. In other words, I didn't see straight no-nonsense physics there -- I saw marketing technobabble couched in nicely looking graphs. In order for me to be convinced of the validity of claimed results, this guy will need to (a) quit averaging fords, chevy's, and dodge results together, (b) show the same graphs with the device replaced with a straight pipe of the same diameter, (c) produce &quot;with&quot; and &quot;without&quot; data for the dodge truck only with a known reputable exhaust system installed already (both stock and 4&quot; performance), (d) prove that all data is directly measured and not calculated, and (e) describe the test conditions and show relevance to real driving conditions.<br><br>One clue that something fishy is going on is the fact that EGTs of over 1200 degrees were measured. That had to have been a modified truck or at least an insufficient exhaust system to begin with. There is no indication that the test conditions even remotely approximate real driving conditions or real configurations that people actually have on their trucks.<br><br>without scientifically valid test results, I have to dismiss the marketing claims. That is, if a manufacturer claims breakthrough science in their product, and then does not use scientific methods to describe the results, then they have no credibilty with me. <br><br><br>expanding the pipe diameter won't increase air velocity. Otherwise, we'd all go out and buy short 5&quot;, or 6&quot; pipe sections and forget about replacing the whole pipe with a 4&quot; system. restrictions are what increases air velocity (remember pinching the garden hose -- energy/power supplied by you and the city water pressure. remember the airplane wing -- energy/power comes from the engine.). The point I'm making is this: in order to accelerate something (including air) you have to apply energy to it. But we're not interested in air velocity per se -- we are interested in air volume movement -- molecules per second out the end. you can do anything you want within a resonator, muffler, or an aeroturbine, but if you don't increase the molecules per second out of the tailpipe's end, then you won't be reducing EGTs.<br><br>The Aero turbine does not appear to be accelerating air. It appears to be nothing more than a sudden increase in pipe diameter and a straight-through muffler or resonator. Without any credible evidence to the contrary I don't think it would be any more effective than any other muffer or resonator of the same major physical dimmentions. In other words, there's no magic.<br><br>The physics of airflow in the intake airhorn is manifestly more complex than putting more &quot;flare&quot; into the pipe to &quot;increase&quot; air velocity. folks have done stuff like that and got poorer resuls too. remember too that boost is not about air velocity either -- it is about air pressure and that is molecules per cubic foot, not molecules second. Of course, we want all cylinders to receive equal manifold pressure, and the airhorn design is optimized for that. By optimized, I mean consistency of air pressure in the cross section of the manifold for a variety of pressures and the air velocities required to acheive those pressures. <br><br>Anyway, when this aerotubine guy publishes valid scientific results, I'll listen. However, at this time my message to aeroturbine is this: don't claim rocket science and then resort to techno babbling verbiage to describe your product. As described, your product appears to be another snake oil attempt to swindle buyers. However, if the results are valid, then publish them with a good valid scientific method so that we can see the real product performance.