Let's talk NVH/Exhaust acoustics tuning

[Cypresser]

To start let's make a goal.

The goal is to figure out what causes the difference in sound to the Maserati Granturismo motor a 4.2 cross plane v8 with a higher pitched and more growl exhaust note... vs ... The base C7 corvette v8 which is a 6.2 cross plane v8 which is has a harsh thumper Harley-esk sound.

Summing up what I think I know thus far...

Compression on the Mas GT is 11.25:1 and the C7 is 11.5:1.
The firing order for the GT is 1-8-4-2-7-3-6-5
The firing order for the C7 is 1-8-7-2-6-5-4-3
Although, as far as I am aware, CR makes little difference, and from what I know firing order obviously can play a huge role here but I'm stuck with what I have on that part.

They both use short tube headers, probably because of space constraints - factory. The GT uses a X-Pipe in the system, while the C7 does not. The C7 uses a valve system in the exhaust where the https://www.amazon.com/dp/B002ONU8A8/?tag=pfamazon01-20. They both have the 4th order v8 sound, BUT the Maserati doesn't have the half order that sound gives the C7 the typical American thumping Harley-esk sound.

The C7 has a 2 valve vs the GT which uses a 4 valve may make a difference. 2 valve systems have a bigger but softer blow down. A single exhaust valve gives a deeper lower frequency noise. More exhaust valves will give it a higher frequency.

As far as internal component weight- the vibration won't translate into reverb into the pipes. Radiated shell noise is something else- you don't want that. You want to engineer the noise from exhaust orifice noise and perhaps intake orifice noise.

As far as difference in dome and port shape and length, port and chamber won't make much difference- it may change the max rate of pressure rise of the cylinder and that leads to high freq combustion noise which you want to dampen out.

Here is a picture of a vehicle semi anechoic chamber for future reference - if it is brought up in this topic.

https://lotusproactive.files.wordpre...09_12_71pb.jpgIn VW world, the 12v VR6 doesn't sound that different than 24v VR6 for example is mute because it's anecdotal unless you have back to back tests in a vehicle semi anechoic chamber with no other changes. VW would have made a host of changes from vr6 12 v vs 24. Honda hemispherical B series heads all sound the same, regardless of displacement. Haven't noticed much difference in changing compression ratio or stroke or bore on a 1.8T, although the VW 1.8T is turbocharged, turbos dampen out and change pulses from the exhaust orifice.

The x pipe shouldn't act similar to what the cross over headers do in that they try to connect exhaust pulses for scavenging also causing the noise change. The reason they shouldn't make a difference is because almost all cross plane V8s have some form of cross over in the system for low speed torque reasons.

For future reference for the Maserati Grandturismo S.

Here the maserati sounds just like an American v8 truck harley-esk sound...

go to 50 seconds in.


VS larini aftermarket exhaust which makes it sound exotic

go to 1:35 in.


Here is the Corvette C7 6.2

This is what most of all the after market exhaust sounds like- which is basically a louder version of the factory exhaust go to 1:00 in.


The corsa Exhaust sound is considered to be the most "exotic" esk sound the C7 has available currently



Maybe equal length shorty headers, keep lengths symmetric to keep half orders down? Any thoughts on this?

 

[Cutter Ketch]

Oh wow! I wish I was rich enough to be able to help. Let me know when it's time to discuss the amplitude vs % of exhaust system remaining in a 1986 Tercel. Now that's a subject with which I have some experience!

 

[Cypresser]

NVH engineering is a real job in the automotive world. https://en.wikipedia.org/wiki/Noise,_vibration,_and_harshness

 

[Cutter Ketch]

NVH engineering is a real job in the automotive world. https://en.wikipedia.org/wiki/Noise,_vibration,_and_harshness

Sorry. Just kidding. I couldn't resist making a joke. I wasn't intending to dis your thread.

 

[Nidum]

I'd expect a 6.2L and a 4.2L engine to sound different anyway . Have you looked at the actual design details and performance characteristics of the two engines ?

 

[Cypresser]

Yes I have. I have them noted here. Performance won't be a tonal difference, just DB.

 

[Cypresser]

Because for whatever reason, this site won't let me update my first post I am updating it via this 3rd unintentional bump reply. See below.

To start let's make a goal.

The goal is to figure out what causes the difference in sound to the Maserati Granturismo (GT) motor a 4.2 cross plane v8 with a higher pitched and more growl exhaust note... vs ... The base C7 corvette v8 which is a 6.2 cross plane v8 which is has a harsh thumper Harley-esk sound.

Summing up what I think I know thus far...

Compression on the Mas GT is 11.25:1 and the C7 is 11.5:1.
The firing order for the GT is 1-8-4-2-7-3-6-5
The firing order for the C7 is 1-8-7-2-6-5-4-3
Although, as far as I am aware, CR makes little difference, and from what I know firing order obviously can play a huge role here but I'm stuck with what I have on that part.

They both use short tube headers, probably because of space constraints - factory. The GT uses a X-Pipe in the system, while the C7 does not. The C7 uses a valve system in the exhaust where the GT does not. They both have the 4th order v8 sound, BUT the Maserati doesn't have the half order that sound gives the C7 the typical American thumping Harley-esk sound.

The illustration shows (for the GT) Exh mani as a 4 into 1 design, shorty, primaries appear to be equal length. X pipe is a ways downstream
http://www.maseratispares.com/1998-heden/images/categories/492_023.jpg

The C7 has a 2 valve vs the GT which uses a 4 valve may make a difference. 2 valve systems have a bigger but softer blow down. A single exhaust valve gives a deeper lower frequency noise. More exhaust valves will give it a higher frequency.

As far as internal component weight- the vibration won't translate into reverb into the pipes. Radiated shell noise is something else- you don't want that. You want to engineer the noise from exhaust orifice noise and perhaps intake orifice noise.

As far as difference in dome and port shape and length, port and chamber won't make much difference- it may change the max rate of pressure rise of the cylinder and that leads to high freq combustion noise which you want to dampen out.

Here is a picture of a vehicle semi anechoic chamber for future reference - if it is brought up in this topic.

https://lotusproactive.files.wordpress.com/2012/11/nvh-anechoic-chamber-exige-s-12_09_12_71pb.jpg

In VW world, the 12v VR6 doesn't sound that different than 24v VR6 for example is mute because it's anecdotal unless you have back to back tests in a vehicle semi anechoic chamber with no other changes. VW would have made a host of changes from vr6 12 v vs 24. Honda hemispherical B series heads all sound the same, regardless of displacement. Haven't noticed much difference in changing compression ratio or stroke or bore on a 1.8T, although the VW 1.8T is turbocharged, turbos dampen out and change pulses from the exhaust orifice.

The x pipe shouldn't act similar to what the cross over headers do in that they try to connect exhaust pulses for scavenging also causing the noise change. The reason they shouldn't make a difference is because almost all cross plane V8s have some form of cross over in the system for low speed torque reasons.

For future reference for the Maserati Grandturismo S.

Here the Maserati sounds just like an American v8 truck Harley-esk sound...

go to 50 seconds in.

VS larini aftermarket exhaust which makes it sound exotic

go to 1:35 in.


Here is the Corvette C7 6.2

This is what most of all the after market exhaust sounds like- which is basically a louder version of the factory exhaust go to 1:00 in.

The corsa Exhaust sound is considered to be the most "exotic" esk sound the C7 has available currently.

How about we turn to something that takes a traditional 90 degree motor (with itbs, dohc heads, and di) that uses tri-y headers and an x pipe factory.

The s65 bmw motor is a lovely motor.
sounds like a small block chev on the dyno to me, buts its the bmw m3 s65 v8.
BMW Engine Dyno - YouTube

Compare that to this full exhaust system by IPE F1


compare that to this
http://www.youtube.com/watch?v=Bzvp...ww.youtube.com/watch?v...&feature=related]E92 M3 Exhaust Compilation - YouTube

Lastly compare those to this
http://www.youtube.com/watch?v=MIsc...ww.youtube.com/watch?v...&feature=related]E92 M3 - Megan exhaust - YouTube

There really has to be more to it than the natural sound of the motor... I would agree that it is more than JUST one thing.

"The crank pin offset is 90°, and for design reasons, a cylinder firing order of 1-5-4-8-7-2-6-3 was chosen for the S65, instead of the typical 1-5-4-8-6-3-7-2 firing order more commonly employed in other BMW V8 engines."

If you can make some sense of that- its odd "Cylinder numbering is 1 through 4 on passenger (right) side and 5 through 8 on driver (left) side. numbers 1 and 5 are at the front, 4 and 8 are at the rear."

Apparently, the firing order is the same as the BMW Sauber F1 team v8.

Check out this s65 header. looks like a tri-y to me.
http://img364.imageshack.us/img364/3289/dscn0632nb7.jpg

http://www.billswebspace.com/DinanE90-92ExhaustDesignReview.pdf

https://www.youtube.com/watch?v=J9u6jI3lRCw]https://www.youtube.com/watch?v=J9u6jI3lRCw
The x pipe from the above video.
http://maxcdn.nexternal.com/aaw/images/Large252.jpg

I think the only reason that the ipe f1 exhaust is higher has to be that x pipe design. which is shown in the following link
http://i244.photobucket.com/albums/gg16/dannyeatworld/20120917_221533.jpg
http://i.imgur.com/batEA.jpg
(not to scale dims) Note the taper of the x pipe and the hole that makes the air pass through a smaller opening on two ends. If you look very close at the x pipe design, its ALMOST as if its two x pipes in one.
http://i17.photobucket.com/albums/b81/BRAAPZ/BMW/X-pipedimsactual2.jpg

Now one thing to consider is the are resonators that cancel out particular noise. this is what Corsa mufflers do. The have chambers in the mufflers (which is more like an instrument than a traditional muffler) that are Helmholtz resonators that are VERY small. They shoot for 3 particular resonate frequencies to cancel out. Now one thing about frequency is that it peaks, there is a range at the peak. The range will depend on many things and without actual testing it is not possible to know the range with math (that i am aware of to date).

http://en.wikipedia.org/wiki/Helmholtz_resonance

In use on an exhaust system
http://forum.grrrr8.net/showthread.php?t=10801]Capped

Now if you actually understand the above link you will see that they are utilizing a Helmholtz Resonator and then packing around it with fiberglass to bring down the vibration(vibration of any kind will bring the volume of the devise up- so this muffles it).

The purpose of a "muffler" is to MUFFLE sound not change the actual tone.

The Corsa I wouldn't even call a muffler per say. I would say it is more similar to the dr. gas freq mod, but a better design.
http://freqmod.drgas.com/]FreqMod]http://freqmod.drgas.com/]FreqMod Mufflers
Corsa cut away
http://s938.beta.photobucket.com/us...938.beta.photobucket.c...jpg.html?sort=3&o=0 As for the 180 headers go, they require too much space and cause heat issues in the confined space. I suppose I should link - this- one of many, videos of a small block Chevrolet (SBC) with 180s sounding exotic as they do. The Kelmarks, grant gts, and many other cars use these headers as well (Ford GT40s too).

Corvette with 180 degree headers
https://www.youtube.com/watch?v=MSZTbR6C6Lw

Now- I just read this entire thread and find more.

http://forums.corral.net/forums/general-mustang-tech/496793-exhaust-drone-completely-gone.html

Here is a copy of the post I made that I was told to start a new thread about.
SO, after reading all of this. I have some questions, some of them I am aware that they were already answered- though to me, they were not 100% clear.

1. "the whole idea is to have the sound wave bounce off the end of the tube and come back 180 degrees out of phase with the original wave thus canceling the resonance. A "1/2 wave tube" would reinforce the resonance - exactly the opposite of the effect being sought. " This statement was made by Michael Y.

I get this statement. One thing for me in particular, I DO NOT care about drone. I care to eliminate particular frequencies, and I care about reinforcing the frequencies that I want. That being said if I had one quarter wave resonator for canceling out the frequency undesired, and then a "half wave resonator" to reinforce the frequencies I want- would they somehow negatively affect each other?

2. It was stated that the frequency canceled (in hz) will not only be canceled at "X" rpm but at higher rpms as well. To me this sounds like what happens when increasing the cfm that, like an instrument, will cause the over-blow effect bringing the frequency up in octaves which then will cancel out out the frequency in higher octaves as well.

Is this statement correct? As I don't care about drone, which is rpm specific, and I care about the actual frequencies that end up coming out of the exhaust tip, no matter the rpm. For esthetic purposes alone for my personal application

3. People appear to be using phone "apps" to measure the DB and the HTZ of the sound of the exhaust. Is there another device (not a phone) I could purchase that does this same thing? If so what is said device called so I can run and go get one?

4. How do I tell which frequencies I do or do not want once they have been analyzed seeing that for me I, again, don't care about drone and this is not rpm specific?

5. Did we ever really have an answer for the heat problem to determine the speed of sound in the device? One thing to note. All engines are different because of the tune, the octane level and many other factors. These will all effect the engine exhaust temperature to a varying degree. Although I think there maybe a close average of what the exhaust temperature could be assumed to be for a performance engine running on pump gas (87-93 octane) that has been warmed up to operating temp and assuming a 65-70 degrees Fahrenheit ambient temperature. That temp was picked because most of us drive fast cars in the summer and we live in America where we do not use Celsius terribly often. Also on a personal note I live in Mn. Daily average summer temperatures in Minnesota range from the low 70s (22 °C) in the south to the mid 60s °F (19 °C) in the north.

6.What is the agreed upon SIMPLE formula (regardless of the final end cap tuning needed) to determine the dimensions of this device? Also I found very little information in the thread in regards to the diameter. As in if and how it makes a difference in the final product of the device. Ie:2 inch dia vs a 3 inch dia vs a 1/4 inch dia.

7. If you go back to the thread that i posted (and now that i understand way more about this because there is some actual genius in this thread) these statements were made.

"That is simply a low-frequency tuning element which has no flow passing through it. Corsa is attenuating frequencies in the sub-200 Hz range to keep its claim to fame of no cabin drone. The simplest possiblity is that it's a Helmholtz tuner with relatively broad tuning due to a short, large diameter throat. The more complicated possibility is it incorporates the convoluted Corsa quarter-wave tuner maze-like device inside the oval shell. Either way, it's a high-pass filter for the purposes of eliminating drone and an "exotic" sound.

The Dinan E92 M3 mufflers that you posted the tech writeup for go one step further with absorptive tuning after the Helmholtz tuning. If you want a more civilized sound, the absorptive tuning will hit the 500+ Hz range. But, after watching FFT plots on my phone during v8 Ferrari clips on youtube, this is exactly the frequency range you seem to desire more of."

He claims that the 500+ range is what I am after.Can I get rid of everything under the 500 plus range? Also, from my understanding of how frequency signal works- it peaks. At that peak it s not just one frequency it is a slight range. Is there a way to calculate that range?

He goes further into saying this;

"As for the calculations surround the quarter-wave tuner, you're in luck because it's simply an open-closed duct. Peak transmission loss will occur at the duct resonance frequencies, f=nc/4L, where c=speed of sound, L=length, n=1,3,5 (odd numbers). This only leaves you to figure out the exhaust gas temperature where you plan to install the tuner and the frequencies that you desire to attenuate.

For instance, at a local gas temperature of 350 deg C, the local speed of sound will be 500 m/s. For a length of 1 m, the lowest transmission loss peak frequency will be (1*500)/(4*1)=125 Hz. The next peak will be at (3*500/4*1)=375 Hz.

If Corsa claims they're only targeting 3 frequencies, that would mean there's only one quarter-wave tuner in the maze device that hides inside their flow-through mufflers. I have reason to believe they're targeting the 210-240, 630-720 Hz, and 1050-1200 Hz ranges. This let's you hear lots of 4th and 8th order content at mid-high rpm (350-500 Hz and 800-950 Hz)."

"n=1,3,5 (odd numbers)"
what is n? and why is it only odd numbers?

"If Corsa claims they're only targeting 3 frequencies"
based on what is he coming up with this?

Note: "This let's you hear lots of 4th and 8th order content"

8. Lastly- How could this device be used with performance in mind as mentioned in this thread on the intake side? I would like to see how this could be helped whilst using a single plane intake and a single carburetor setup. As you could postulate, that is what my engine has. Also I have seen threads in regarding g35s using "VHR Advanced Resonance Tuning Test Pipes " and apparently seeing a difference in tq (and seeing that hp is a function of tq...), minimal but still. The same can be said for the Ferrari F1 team, they are using a Helmholtz res on their exhaust. This tells me that perhaps the resonance is affecting the engine harmonics in a way that is positive in nature?

Maybe equal length shorty headers, keep lengths symmetric to keep half orders down? Any thoughts on any of this?

 

[Cypresser]

I happened to come across a device today that actually solves all of this! See the following links and info.GOT IT!

8-1 collector. I almost don't care how it works- although, I do. I can't find too much info as to why it works though.





http://betawpe.fabricationlife.com/wp-content/uploads/2011/04/photo-3-500x375.jpeg



used on the tanner faust's drift car (900hp LS corvette motor)
http://www.pro-touring.com/threads/114542-8-into-1-header







https://www.youtube.com/watch?v=w3dEbOC3G_M
underbody of c7 to see where this collector would go.
https://www.agency-power.com/wp-content/uploads/AP_Stingray2-32.jpg

http://www.racemufflers.com/1-5-8-Primary-8-into-1-Base-Merge-Collector-p/8b-1.625-304.htm

and YES I have verified that it has to be the primaries and one can't just do a y pipe off of a headers to a single exhaust see this example

https://www.youtube.com/watch?v=DXzBC2DYWsY

How would you make them 2 piece?
would need to split the primaries off with a flange basically

https://www.japspeed.co.uk/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/z/z/zz02758-01.jpg

this is not a great example because its 4-2-1 header. but it has a flange where the 4 (flange) 2 go then it goes to a collector after the 2-1

so 4 (flange)2(collector)1

ours would have to use 2 stacked on top of each other and welded to make a single collector 4-1 style

http://www.coneeng.com/images/collector/new1.jpg
but then we would need flanges coming from each side going into the collector basically. so kind of liek treating the collector like it is a single big ass cat that Ys up to each header but each y will have 4 tubes joining primary tubes Modifying long tube headers would probably be a really easy way, cut the tubes make a custom flange then just extend the long tubes.

they make long tube headers for vettes

i think we would need a more flat collector though than that - 8 in a circle- kind

https://www.kooksheaders.com/news/kooks-corvette-c7.htmlFriggen problem- friggen solved. Although, I would really like to know WHY/HOW this works. I assume that it somehow equals out the exhaust pulses once it comes to the one collector.