Exhaust design and muffler placement.

[endeffect0]

This is a fairly simple question that has turned out to be difficult to answer.

Q1)
What affect does muffler placement have on the sound of an exhaust?

I have a 3 inch turbo back, the first half of which is my own design and the cat back is a greddy evo II unit put on by the previous owner. I am very happy with the sound of it but I want to move the muffler further inboard because i am sick of looking at it and scraping it along the ground. This is no fart can exhaust, I love the sound and the look is pretty good but i want it moved.

In asking around its clear that in most peoples experience its hard to differentiate between the effect of muffler deign, muffler placement, and raw engine sound.

ex. A common train of thought would be this: Most older muscles cars and even newer v8 cars with throaty sounds have mufflers mounted way inboard and with their aftermarket exhausts have just a single muffler usually mounted several feet from the tip.
... this sort of approach to the problem does not separate effect from cause.


Q2)
I would like to move my muffler to the location previously occupied by the cat. While clearly a completely strait exhaust would flow better, how does the placement of a muffler affect its restriction on exhaust flow. it seems logical that any restriction closer to the turbo would have a grater effect on performance but is their any fact to this?


I nearly forgot to post this. This was the result of a previous exhaust i fabricated for my mr2. its mufflers are mounted before the Y pipe just about 3 feet down stream of the turbo. It sounds pretty friggin awesome. this is science.

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[Rob10_99]

Since your AWD your pretty limited in options. The only real muffler you could stick under there besides the stock place would be a resonator. If your thinking of using some type of resonator that isn't a direct shot in/out I don't think you could fit it under there.

Well, the closer the muffler is to the head, the more energy it has,(the exhaust gas) so I would assume if you had some type of noise or resonance canceling muffler it would do a better job than if it were all the way in the back where the exhaust is fairly cold.
Heat+ velocity are where the noises are going to get the best cancellation from what I've found.

I made my own 3" as well, it's just a straight shot all the way to a 3" summit flowmaster type muffer(total ripoff, but dirt cheap). I had one of those 'open header' twisties in part of the straight pipe, and it seemed to hold back a lot of pressure. I don't think they were made for turbo cars with too much exhaust to get rid of.

 

[LiquidX]

I want to join in on this thread as well as opposed to making a new one. I'm having a shop do my catback which will consist of 2 resonators (1 louvered and 1 perforated), 1 5" round Magnaflow and the end muffler Magnaflow single in/dual out. All of it is 3" and straight though.

Will I have a sound difference if I have the exhaust welded up as so:

5"---Perf---Louv---End (I feel this will be the best setup)

as compared to

Perf---Louv---5"---End (Or would this be quiter with lower drone?)

Will it matter at all how they are lined up?
I'm looking for the lowest dB possible and having the lowest drone possible. The resonators are mixed because I was sent the wrong one when I made my first exhaust and didn't mind about having a little better sound suppressing.

 

[123abc]

Last semester at school we welded up my friends cat back on his 92 Legacy Turbo. He got a 3in. hks downpipe and 3 inch piping to a cherry bomb glass packthen just more 3 inch piping angled out near the stock location. I must say it has a GREAT sound. Its not too loud either until you get on it.

I plan to do the same exhaust soon. I'll try and remember to post a video.

 

[LiquidX]

Last semester at school we welded up my friends cat back on his 92 Legacy Turbo. He got a 3in. hks downpipe and 3 inch piping to a cherry bomb glass packthen just more 3 inch piping angled out near the stock location. I must say it has a GREAT sound. Its not too loud either until you get on it.

I plan to do the same exhaust soon. I'll try and remember to post a video.

So did they teach you about exhaust acoustics at all? Will my setup have different tones depending on their placement on the cat back?

 

[pboglio]

One practical problem is muffler packing is affected by heat. Placing them closer to the motor will wear them out sooner. So far, I haven't had a noticeable problem with my mid muffler near the cat in terms of packing breakdown.

Moving exhaust components around has always been a case of managing heat loss as in the case of cats needing to be closer to the heat source, and mufflers being moved away from them. Some tuning differences I'm sure exist, but pulse tuning in the exhaust stream on turbo cars is much less a factor than on N/A cars.

I firmly believe its a case of weight distribution, as a 15-20 lb muffler definitely is needed more at the rear of your typical car then in the middle.

 

[LiquidX]

So I could go with my orginal plan with the 5"--res--res--end muffler. The cat will be before the mufflers as well so the heat issue will be fine and everything is 3" straight through. I just think that if you muffle the sound before it hits the resonators the incoming resonance will be reduced as well. Reducing the work on the resonators to allow them to work better and lower the overall resonace not to mention greatly reducing the dB before everthing else. I just want to know if my theory is theory or infact, fact.

Just want my exhaust to be the quietest as posible with my combination setup with any possible reduced resonace as well.

 

[RipperXX]

I have a caless 3" system with 2 resonators and straight threw muffler, it has a nice deep tone, but is still loud.


If you really want quiet, just put on a 3" DP and put the rest of your stock exhaust on, and just use a cut out at the end of the DP. This way you can ride around with just slightly louder than stock exhaust, but open the cut out and open it up when need be.

 

[LiquidX]

I have a caless 3" system with 2 resonators and straight threw muffler, it has a nice deep tone, but is still loud.


If you really want quiet, just put on a 3" DP and put the rest of your stock exhaust on, and just use a cut out at the end of the DP. This way you can ride around with just slightly louder than stock exhaust, but open the cut out and open it up when need be.

That's good and all if you don't have emissions. Thanks anyway. Even though that would give you stock sounds, I'd rather have my 3" performance 100% of the time and still be reasonably quiet.

 

[pboglio]

Here's a little write up I did years back which seems appropriate for this thread:

http://www.dsmtuners.com/forums/art...164893-thermal-r-d-exhaust-review-2g-awd.html

You can put all the resonators you like in an exhaust system, but if your main muffler is small in volume, it'll still be loud. A louvered core resonator is a very bad idea. Usually 1 large and 1 small resonator and main muffler are used for good sound control. I took the opportunity to place a 5 inch muffler where the resonator would go, boosting my muffler volume up substantially and also serving as a resonator.

If I were to do it over again, I'd probably go to a smaller diameter single exhaust tip or possibly even a dual tip though the backpressure would increase.

Sound proofing the rear hatch area would pay huge dividends. Every time I drop the rear seatbacks forward the db level increases dramatically. A careful application of dynamat or the like would be all I would need for a daily driver. YMMV.

 

[LiquidX]

Here's a little write up I did years back which seems appropriate for this thread:

http://www.dsmtuners.com/forums/art...164893-thermal-r-d-exhaust-review-2g-awd.html

You can put all the resonators you like in an exhaust system, but if your main muffler is small in volume, it'll still be loud. A louvered core resonator is a very bad idea. Usually 1 large and 1 small resonator and main muffler are used for good sound control. I took the opportunity to place a 5 inch muffler where the resonator would go, boosting my muffler volume up substantially and also serving as a resonator.

If I were to do it over again, I'd probably go to a smaller diameter single exhaust tip or possibly even a dual tip though the backpressure would increase.

Sound proofing the rear hatch area would pay huge dividends. Every time I drop the rear seatbacks forward the db level increases dramatically. A careful application of dynamat or the like would be all I would need for a daily driver. YMMV.

I got the secondary muffler idea from one of the threads and used this muffler in it as well. I'm not concerned about the 5% loss of flow from the short louvered resonator. My exhaust was actually VERY loud with a 3" highflow cat, 2 resonators and a dual 3" outlet 18" Magnaflow. All I'm doing is just adding in the 5" round muffler. I know that volume is what will control the dB and that's why I got the other muffler to add in. I was just more curious if placement would affect the sound; both dB and resonance.

 

[pboglio]

Have you ever questioned WHY your exhaust system is still loud? Your worrying about trivial positioning of components that may or may not buy you anything. If it was loud with a 3" cat, 2 resonators, and a main muffler, I can say that you selected the wrong sized main muffler. I have no problems at all with resonance or db levels running zero resonators and no cat, thanks in large part to the massive main muffler and the biggest mid muffler that can physically be fit under a car. The KISS method works.

 

[LiquidX]

Have you ever questioned WHY your exhaust system is still loud? Your worrying about trivial positioning of components that may or may not buy you anything. If it was loud with a 3" cat, 2 resonators, and a main muffler, I can say that you selected the wrong sized main muffler. I have no problems at all with resonance or db levels running zero resonators and no cat, thanks in large part to the massive main muffler and the biggest mid muffler that can physically be fit under a car. The KISS method works.

Well the next size up is the biggest one they have which is 22" for the single in, dual 3" out. It's not that it's very obnoxis loud, it's just too loud for my personal taste. Adding in the second muffler will decrease the sound and I've needed a new exhaust regardless. I just want to know if placement order actaully does infact change sound. I just want close to stock sounds and I sent you a PM as well

 

[pboglio]

To keep things brief, yes, the 2nd muffler will make a large difference. Not all mufflers are created equal though. Some of the loudest mufflers I've owned were Borla's and I don't like them because of this fact but sometimes you go with whats available.

When the muffler is a thin oval style, there isn't enough room to put the fancy foam sound insulation like the foam cubes that Greddy used/uses, just the steel wool packing and maybe a fiberglass blanket. When its a big muffler, you have the bigger volume, then the far superior sound insulation material added.

My neighbor runs his EVO exhaust with a small resonator in place of the cat, with a canister style muffler. It is a very very loud exhaust system and I feel the need to actually put ear plugs in when I drive in his car.

 

[casperfast]

my 2 cents....

whil i was going to school in sacramento i was working at flowmaster, i started as a welderon the assembly line, then i began looking into the designs. at the time i had my 2g tsi and i wanted to do a flowmaster system on it. whati was told during my sit down with head of R&D in engineering is that for our cars there is aspecial resonator/tip they make just for the turbo dsm to instal a flowmaster muffler. it puts the muffler in about 10 in more my utilizing the bend and the tip is 8 in long to prevent ANY cold air from re-entering the exhaust system which causes the gas to expand further and restricts the flow. also you need to keep in mind that the exhaust coming out of the cat is way hotter than when it enters..... sounds strange but i promise, due to the catalitic reaction inside..... just a thought. i am planing on running a 3" dp to my cat, then off the cat 10" of 3" pipe into a large cherry bomb, then over the rear and into a small cherry . ill let ya all know how it turns out. i will also be running dyno before and after.

forgot: also when i was testing aftermarket parts for nopi at my school we had the greatest gains with glasspack mufflers, not canister or baffled type on everything we tested

 

[pboglio]

Keep in mind that the Flowmasters are a reflection style muffler and not the quietest design around, and nowhere near the least restrictive. Some guys have had luck with "active" mufflers but I like keeping things simple.

Big, straight thru perforated core, high quality muffler in the rear, then a 5" dia bullet muffler in the midpipe, done. If I could fit another bullet muffler in the position where the cat goes it would be almost boring quiet, but it could be done. You need more quiet than this then you need to check for a pulse.

 

[endeffect0]

WOW! this thread really blew up since i last checked. I would like to comment on quite a bit so forgive me if this post gets a little muddy.
(Warning: Long Post to come)

5"---Perf---Louv---End (I feel this will be the best setup)

In my opinion that is the setup i would use. louvered resonators flow approximately 5% less than their perforated counterparts. might as well put that latter in the setup to reduce its limiting effect. i would guess the total sound cancellation (aside from a suspected tonal difference) would remain very similar.

Last semester at school we welded up my friends cat back on his 92 Legacy Turbo. He got a 3in. hks downpipe and 3 inch piping to a cherry bomb glass packthen just more 3 inch piping angled out near the stock location. I must say it has a GREAT sound. Its not too loud either until you get on it.

I plan to do the same exhaust soon. I'll try and remember to post a video.

Thats more or less the exact thing I did with the above MR2 .. only its much shorter..... and very loud. IF i could get the same sounds, at less DB out of the DSM it would be perfect. See if you have that video i would love to see it.




Pboglio: thank you for all your input into this thread!

One practical problem is muffler packing is affected by heat.... So far, I haven't had a noticeable problem with my mid muffler near the cat...

I firmly believe its a case of weight distribution, as a 15-20 lb muffler definitely is needed more at the rear...

Agreed on both points. In the past I helped fabricate a series of exhausts for a 3 rotor powered lotus 7... as i am sure most of you know rotorys run much hotter than normal engines. we fabricated the entire length of the systems from the 4inch down-pipe to the exit, completely out of glass packs. about 4 feet. we had a hard time finding resonators rated high enough to withstand heat.

im sure i have pics if anyone would be interested.



On the link you posted.
the the discussion of muffler volume is quite interesting. unfortunately my experience with exhaust system design is more in the direction of NA systems. In the case of the na motors as far as the engine is concerned the exhaust is made up of two components that affect it. the header junction, which ends several inches after the union and has the combine affects of header length, tube diameter, comparative length all of the bends and the junction that brings them together. From that point back, all the exhaust sees is the length to the muffler, assuming the muffler is of sufficient volume the exhaust is done. from that point on it doesn't matter if you have 3 inches of pipe or 5 feet, assuming it flows better than the muffler is self the engine considers anything past the muffler to be atmosphere.

(ignoring the cat in both cases)

I think things on a turbo car things are a bit simpler. either a few inches off the back side of the turbo or where the waist gate dump comes back in is the end of the manifold region, from their on all the car sees is the muffler. in the case of your twin muffler system i suppose all that would matter would be the more restrictive one. If it is placed first from their back is atmosphere, if it is in the second position then the total restriction after the manifold would be ended at that point.



In regards to my original question then, I am not looking to quiet my car down. the setup i have is very pleasant, not raspy at all and has a good deep tone. I have not heard a better sound from another dsm that i have met.
However, i hate the can greddy has hung off the back of my car. I believe the POA at this point is to relocate it to the previous home of the cat, assuming I have room.
Seeing as the change in tonal quality seems to be an unknown, what's the consensus on the mufflers life expectancy in that location? clearly it will be hotter, but will i deep fry the muffler packing?

 

[pboglio]

A good book if you haven't picked it up on exhaust system design is "Scientific Design of Exhaust & Intake Systems, by Philip H. Smith and John C. Morrison. Goes into alot of empirical data on types of mufflers, tuned lengths, tons and tons of empirical data.

I'm not saying repositioning of the mufflers doesn't have an affect on "sound" tuning, but it simply isn't mentioned that I can find.

First clarification is that: Resonators and Mufflers are close to the same thing, some resonators are packed with sound dampening material, effectively making them a skinny muffler, and some are simply straight thru perf. tubes with empty chambers, like a primitive muffler.

Inside mufflers sounds waves are dissipated literally by bouncing them off the packing material, being absorbed thru friction, and the sounds level amplitude being consequently reduced. So, having a deep layer of packing material is critical, and is common sense. Also mentioned is the fact that mufflers/chambers in series are far more effective than just one large muffler of equal volume. By "large muffler" I think he is referring to a large diameter muffler of a certain fixed length. So having a large diameter muffler as the main muffler, and another muffler of similar "length" has a much larger affect on reducing sounds levels, then a single muffler of equal volume. The problem is that increasing the length increases pressure loss.

On page 122, Fig 6.5 I think is what everyone wants to really pay attention to.
Tests were done with a straight perf pipe with ZERO packing material (empty muffler), then a regular straight thru core muffler, then 2 regular straight thru core mufflers in series. DB levels are measured here is "psi". The first muffler produced about 1.25 psi peak amplitude that had very little wave "decay". 2nd muffler design had a peak amplitude of .75 psi with faster decay. The 3rd "set" of mufflers were down to .4 psi with decay 1/2 that of the 1st muffler tested.

So, from this one can conclude, multiple mufflers in series have a large affect on sound dampening performance. And this is exactly what I noted on my custom exhaust system. I can say from personal experience, 2 high quality mufflers is more than sufficient, if a 3rd muffler or at least a big resonator could be fitted, I think you would achieve as much reduction in noise levels as is possible and the graphs show diminishing returns.

My own conclusion is filtered down to: 1) Muffler packing depth has a very positive affect on sound amplitude reduction, with diminishing returns as packing material depth increases (test data provided in book. 2) Muffler length does NOT affect frequency, but NUMBER and AMPLITUDE of pressure peaks. The AVERAGE of the peaks is less, with the 1st amplitude being the largest, then rapidly diminishing amplitudes, and less of them. This is what your ear "hears" anyways, an AVERAGE, especially when the sounds pulse are hitting you every 20 millisecs.

As far as resonance is concerned, it is mentioned but the fact is if the amplitude is being reduced, does it really matter if there is resonance? A resonating chamber is shown and tested with inconclusive results but in my opinion the method laid out with series mufflers makes a resonating chamber redundant. Its done on intake systems but then again they don't run ANY mufflers.

Buy the book, then go design your exhaust system

 

[DSMunknown]

http://www.dsmtuners.com/forums/bol...stealth-muffler-axle-back-exhaust-system.html


After experiencing the Db difference between the Vibrant Performance and Thermal mufflers, I contribute the diffence to a number of things. Firstly, the quality of the materials used and how well the material is packed. Secondly, the use of two smaller perforated cambers versus one larger one. Thirdly, as pboglio stated, the actual volume of the main muffler. Other stuff skips my mind, but those would be the top three things that currently strike me as important to note.

If you're stuck on staying with a 3 inch system, that's fine. But has jusmx141 has repeatedly stated, full 2.5 inch piping is still an upgrade and will last most people, as well as bring the Db levels down. Believe me, I love my full 3 inch system, but with the cops constantly on my ass in & around town I gotta be stealthy and a few steps ahead of the game. Because the 2G is down for a long while, I may seriously consider "downgrading" to a full 2.5 inch system. Will still have a performance-minded exhaust system, but without the extra Db levels that naturally come with a 3 inch system, especially when I only have (currently) one muffler in place.

 

[LiquidX]

I would like to know your reasoning behind using 2 smaller mufflers/resonators would be better than 1 larger one. I know I was asking this further up in the thread but it started to make sense. The smaller the muffler, the less packing there is within it to absorb the dB from the engine. Regardless of having 2 small mufflers, they will still be limited overall to how much sound can be suppressed. A larger muffler can be made with a better design overall and better sound suppressant material.

So I believe that the larger (quality) muffler will surpass 2 smaller mufflers in conjunction with a main muffler.

 

[Morphius]

Will my setup have different tones depending on their placement on the cat back?

Simply, yes.

 

[pboglio]

I would like to know your reasoning behind using 2 smaller mufflers/resonators would be better than 1 larger one. I know I was asking this further up in the thread but it started to make sense. The smaller the muffler, the less packing there is within it to absorb the dB from the engine. Regardless of having 2 small mufflers, they will still be limited overall to how much sound can be suppressed. A larger muffler can be made with a better design overall and better sound suppressant material.

So I believe that the larger (quality) muffler will surpass 2 smaller mufflers in conjunction with a main muffler.

Yes, but as you go bigger the packing depth gives less and less assist. Thats why even 2 smaller mufflers in series can still surpass a huge one of equal volume. You want to give the sounds waves an opportunity to bounce "into" the little perf holes, longer core length allows that. Once they are in, say for illustration that 50% of the packing depth is doing 75% of the work, the last 50% for instance is doing much less work. Its a case of diminishing returns.

The point is to allow the opportunity for a) having the sound waves bounce into the packing, and b) maximize the kinetic energy dissipation when the sound waves are actually IN the packing. Core length helps out situation a), and core depth helps out situation b). This is exactly what the book illustrates and I think its a safe conclusion to draw from the data.

DSMuKnown mentioned his twin exit muffler. Similar scenario, both mufflers looked of equal volume and equal core length, but the twin exit is clearly quieter. My feeling is that the smaller diameter internal twin pipes, had a net effect of shifting the frequency(s) up higher, that means the waves are closer together, and for a fixed length muffler, increases the chances of the sound waves dropping right into a perf hole and letting the packing do its thing. Though each smaller pipe has to share half the muffler packing, it still ends up being quieter. Edelbrock has a muffler just like this but I don't like the flow loss of doing a y-split into the muffler. Everything is a compromise.

There are a few "bypass" style mufflers that send exhaust into and out of the muffler, then loop it back around thru it again for a 2nd pass, looks sorta like two tubes thru one muffler, but one tube has a big loop. Same principal, not all the sounds waves got dissipated on the first pass, so the second pass gets the majority that didn't make it in on the first. This may be an option for guys with space constraints, food for thought.

Another example is the Dynomax style internal "S" turn mufflers. Essentially an long internal style muffler, with the addition of an expansion chamber to deal with resonance. Obviously, didn't work cause they were a loud ass muffler, but the design in theory makes sense aside from the pressure loss associated.