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Active NSX Exhaust System

Mac Attack said:
All of the exhaust piping in cars has a certain length, usually governed due to space and layout requirements. The NSX is pretty unique because there is so much space right behind the engine to play with and manipulate the sound. Now, the length of all that piping has it's own resonance frequency and contributes to the overall tone of the exhaust leaving the tailpipes. So, all the resonance frequencies due to the lengths of piping from a collector to a cat, cat to an x-pipe, x-pipe to a muffler, muffler to the tailpipe, etc. all sum up in the end. Of course, relative sound volumes will be different due to changes in piping area, and whether or not it will have a muffler or restriction to dampen that frequency later downstream.

An earlier post by ryu in another thread had questioned if the tone of this could be changed to make it nicer sounding. I replied that I didn't think much could be done - only to dampen the unwanted frequencies to make the pleasant stuff come through better. I may have been wrong. What I'm going to try next is a small final "chamber" where all the exhaust dumps into, whether it's in quiet or rowdy mode. This chamber will then have four 1.75" diameter tailpipes, each with a different length tuned to the frequency I want to resonate at various RPM's (highlighted in the spreadsheet).

I don't know if it will work or not, or resonate that much louder than all the other stuff coming out. To keep it simple and make it easier for me, I'll have to modify my existing setup. A sketch is below on what is next.

It will be about 2.5-3 weeks though before I can weld this up and try it out. Some other stuff has come up so this will unfortunately have to wait a bit.

Theoretically, at 3000 RPM, the ~23 in long tailpipe will resonate with the engine firing rates 2nd harmonic of 300Hz. Hopefully, this will allow a higher frequency third harmonic to be heard as well over the rest of the exhaust. Likewise for the other three tailpipe lengths to emphasize the 2nd engine firing rate harmonics at 4000, 5000, and 6000 RPMs. I didn't choose anything to highlight above 6000 RPMs since the rest of the broadband engine noise will drown it out.


resonances.JPG




Sorry about the crude sketch - this is what I'm trying next. It should only weigh just a little more than my 21lbs now because of the extra 1.75" tailpipe piping. The small 6" long 3" diameter straight-through muffler will be removed.

modified.jpg


Dave
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Dude... I hope you succeed.. everytime someone pulls off something big... it was because "they didnt know if it would work"... if it does.. you win!

I respect you... mainly because you research things to highest level before you "start"

secondly... because you actually try it!

Good luck and were here to help if needed..

Regards
 
StmpoRaceProducts said:
Dude... I hope you succeed.. everytime someone pulls off something big... it was because "they didnt know if it would work"... if it does.. you win!

I respect you... mainly because you research things to highest level before you "start"

secondly... because you actually try it!

Good luck and were here to help if needed..

Regards
Click to expand...
Ross - you hit the nail on the head. +1 amigo. I've also already mentioned to Dave that i'm here to help.

and well.. for us backyard hobbyist, this is fun stuff too.
 
Brainstorming. :tongue:

Maybe the "howling" sound is generated by the exhaust flow itself - not the engine. So its not an issue of isolating and emphasizing certain frequencies of the engine sound - its a matter of creating new ones. Maybe its based on the same principles as when you blow air past the opening of an empty beer bottle?

This might actually be of some interrest when it comes to "designing" the an LF-A-like exhaust sound:

http://www.phys.unsw.edu.au/jw/woodwind.html
 
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RacingHeart:

You're exactly right - as long as you have some airflow, you can generate different tones based on how long the air columns are for the air to resonate in. The frequencies depend on whether or not one end is closed, both ends are open, if the tube is conical, etc. It gets pretty complicated!

The problem is picking out what frequencies are pleasing, and what aren't. Then, you have to take into account harmonics, i.e. a closed standpipe has harmonics every odd integer (1,3,5,etc), while an open standpipe has harmonics every integer (1,2,3,4,etc). The harmonics makes a difference in what we each find pleasing - the absence of even harmonics will tend to give a "hollow" sound that some people may love (clarinet), but others dislike. We're all unique!

Now, the idea with picking up on the engine firing rate is that it is a dominant frequency at a given engine speed. It's usually 10dB louder than the other broadband exhaust noise on a straight-through system. On the LF-A muffler spectrum, they've plotted muffler noise as a function of engine speed, and have circled the dominant Engine Firing Rate (EFR) frequencies for the fundamental harmonic (and the 2nd and the 3rd). You can see that the fundamental EFR is the loudest (brightest yellow points). Then, they've been able to tune the muffler to somehow resonate and amplify the 2nd and third harmonic frequencies.

So, to compare the LF-A V10 to the NSX V6, at 3500RPM's the fundamental, 2nd, and 3rd harmonic EFR frequencies (Hz) are:

Fundamental 2nd 3rd
LF-A: 292 584 876
NSX: 175 350 525

Look at the LF-A muffler plot. Trace over at 3500RPM's, and you'll see the dominant muffler noise is at 292Hz, 584Hz, 876Hz, and some additional noise at 1200 and 1800Hz. To get this tone, our NSX (with an LF-A muffler) has to be spinning at 6000RPM.

So, it's generally given that we like the higher frequencies from our exhausts without any "rasp." In order to highlight those frequencies, one method should be using tailpipes of various lengths that resonate at the desired frequencies.

Now, I don't particularly want to resonate our low frequencies and make them stand out any more than they do already, so I'm hoping to target four frequencies (the 2nd harmonics at 3000, 4000, 5000, and 6000 RPMs) and make them resonate a little louder so you can hear them over the rest of the exhaust noise and hopefully even louder than the primary frequency.

Only four were chosen because it's impractical to have a bunch of tailpipes sticking out the rear. 3000RPM was chosen as the lowest range because 90% of my driving is cruising around less than that engine speed - I don't want a loud exhaust noise even at a "pleasing" frequency for any part of my daily driving. 6000RPM was chosen as the upper range because above that, our engines just make so much clattering and broadband noise it just didn't seem practical.

Finally, it's important to have the engine sound to change tone as you accelerate because it gives a sense of power. Hopefully, four resonance tones will be enough (combined with the primary EFR frequency), that will give nice tones at 300, 400, 500, and 600 Hz when I want it to get a little sporty over 3000 to 6000 RPM's.

You can tune it for higher frequencies (the 3rd harmonic), but I was worried the amplitude (volume) wouldn't be loud enough to make it resonate and stand out above the rest of the noise. If this idea resonating the 2nd harmonics works, then maybe someone else can try resonating the third harmonics :smile:

Dave

(p.s. - my parts will all be in tomorrow. I can do most of the fabbing during the week and then hopefully weld next weekend....)


RacingHeart said:
Brainstorming. :tongue:

Maybe the "howling" sound is generated by the exhaust flow itself - not the engine. So its not an issue of isolating and emphasizing certain frequencies of the engine sound - its a matter of creating new ones. Maybe its based on the same principles as when you blow air past the opening of an empty beer bottle?

This might actually be of some interrest when it comes to "designing" the an LF-A-like exhaust sound:

http://www.phys.unsw.edu.au/jw/woodwind.html
Click to expand...
 
Dave, it looks like your final design will still use the 1/4 wave tube design to help eliminate the nasty 105hz drone. If you're not using an RPM activated bypass valve i'm not certain why you need one at all. Is it just for amplitude control?

If your version works by amplifying the 2nd harmonics, you betcha, yes sir, I will give the 3rd and possibly the 4th a good go.

btw.. reading through your posts makes me feel like I have a small brain. Which is good! but also probably true :)
 
I feel like a gernade just went off in my brain!! :eek:

Amazing that you guys are out there and understand this. I get everything else about cars except for the transmission and tunning of exhaust.

+100 on the R&D and work you have done!
 
RacingHeart said:
Just found this and i thought it might be worth a look for you.

<object width="640" height="385"><param name="movie" value="http://www.youtube.com/v/3y_XPqBMqv0&hl=sv_SE&fs=1"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/3y_XPqBMqv0&hl=sv_SE&fs=1" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="640" height="385"></embed></object>

Amazing sound, And its interresting to see how much difference an X-pipe makes - even on a Ferrari.
Click to expand...

About 2years ago I contacted Capristo and they said they would make a NSX exhaust. They just needed to loan a car to test (test car gets reduced price) and dyno and at least 10 buyers upfront. This was before all the belcanto stuff hit the markets. But ended up as a no go since everyone flakes out.
 
RYU said:
Dave, it looks like your final design will still use the 1/4 wave tube design to help eliminate the nasty 105hz drone. If you're not using an RPM activated bypass valve i'm not certain why you need one at all. Is it just for amplitude control?

If your version works by amplifying the 2nd harmonics, you betcha, yes sir, I will give the 3rd and possibly the 4th a good go.

btw.. reading through your posts makes me feel like I have a small brain. Which is good! but also probably true :)
Click to expand...

Good question. When the cutout is closed for quiet mode, all that unused 3" pipe will still act as the quarter wave resonator to cancel that annoying 105Hz drone between 2000-2500RPM. Since a lot of stop/go and city driving between 40-50MPH is at 2000-2500RPM on my 5speed in 5th gear, it would drone a lot when I want it quiet.

If your quiet mode is really quiet (like you had a heavy muffler on there) and restrictive, then you wouldn't need this resonator since all the frequencies would get attenuated by the big, heavy muffler. But, because I still wanted to keep this light and small, my single cat and single 2.25" pipe isn't really that quiet (see the first post where I did the sound dB comparison). It's not bad with the windows up and you can't hear it just cruising around over 40MPH with a light load. But I still wanted it a tad quieter. That's why I think adding on this last section of pipe will quiet the quiet mode even more (since going from a 2.25" pipe to a 3" "chamber" is technically an expansion section and will act as a low-pass filter). Hopefully it will be just right :wink:

UPS had a snag so I just got all my parts for this last Monday. Maybe I can start cutting some pipe tonight, but I doubt this will get done by this weekend now.

Dave
 
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Hey dave,

How hard is it to take an existing exhaust and cancel out the 105hz droning? Ie, if you had a taitec GT Lightweight, how hard is it to rid it of drone? Is it a lot of modifications?
 
Soap said:
I feel like a gernade just went off in my brain!! :eek:

Amazing that you guys are out there and understand this. I get everything else about cars except for the transmission and tunning of exhaust.

+100 on the R&D and work you have done!
Click to expand...

Thanks, but the Version 3 of this isn't working yet :biggrin: I'm kind of having doubts now, but hopefully we'll be pleasantly surprised soon!

As an engineer, I listen to fellow engineers talk out their a$$ all the time about stuff they don't know or understand. They make stuff up to cover themselves and "save face."

I'll be the first to acknowledge I'm not an acoustics expert and this is my first real venture into designing an exhaust system. From my understanding, all these cool car manufacturers spend a bunch of money and time designing an exhaust system in CAD and acoustic analyzer programs, and then fine tune them in real life through countless hours on a dyno in an anechoic room taking sound measurements :eek: I'm just a hack with no experience in this field, and just enough knowledge to be dangerous :smile:




rasir_x said:
About 2years ago I contacted Capristo and they said they would make a NSX exhaust. They just needed to loan a car to test (test car gets reduced price) and dyno and at least 10 buyers upfront. This was before all the belcanto stuff hit the markets. But ended up as a no go since everyone flakes out.
Click to expand...

Yeah, that's the problem with this small market and the source of many vendors' frustration. That would have been neat, but expensive I'm sure :eek: Capristo makes some nice stuff.




NetViper said:
Hey dave,

How hard is it to take an existing exhaust and cancel out the 105hz droning? Ie, if you had a taitec GT Lightweight, how hard is it to rid it of drone? Is it a lot of modifications?
Click to expand...

First, are you sure it's 105Hz? Is it only between ~2000-2500RPM? If so, you would have to put a resonator on each of the exhaust banks' piping (unless you were to cut up the single cannister and try to figure out a way to attach a single resonator to it). Quarter-wave resonators (straight or curved tubes like I've done) would be too long, so you would have to do two helmholtz resonators to save space. Unfortunately, this adds weight, but probably no more than 10lbs in SS. It would also be a pretty $ to do it, unless you could convince some of our fine vendor/fabricators on here to do like an exchange program.

I'm guessing it could look like this:
attachment.php




Dave
 
NetViper said:
Hey dave,

How hard is it to take an existing exhaust and cancel out the 105hz droning? Ie, if you had a taitec GT Lightweight, how hard is it to rid it of drone? Is it a lot of modifications?
Click to expand...
I've had many PM conversations with Mac Attack about doing a similar thing for any given exhaust. I'm surprised he still answers my PMs since I just play a rocket scientist on TV and haven't had any real technical training! I was more interested in proving my methodology thru some type of proof-of-concept.

I hope Mac would agree with this high level methodology. Since you're probably the drone eliminator pioneer for your particular exhaust (every exhaust is different) you will need to start in the beginning.

1. You will need a good microphone and a recording device (i.e. laptop) and a good sound analyzer. This will allow you to do a few recordings in the RPM range you want to isolate a particular sound wave(s) from. In this case, Mac noticed his "drone" was occuring mostly in 2000-2500 rpm and I believe he said in the past it was 105hz. The drone in my Chevelle for example is real nasty around 115hz I suspect. By the way the difference between 90hz-120hz is a big enough variance to throw off your calculations which you will see in later steps.

Note: Having an existing exhaust to start with makes thing so much easier since it gives you a starting point. Starting from scratch is tougher.

2a. Once you isolate the particular frequency you want to deemphasize (or emphasize) you can use either a heavy muffler, a Helmholtz resonator, or a 1/4 wave resonator to "tune". This is where the calculations come in.

2b. You then need to figure out how to package your solution. A Helmholtz is complicated to calculate but it lends itself to more compact packaging (I would need Mac's help for sure if I ever went down this path), or a simpler 1/4 wave resonator but they tend to get long the lower the hertz you want to isolate and a few other variables like if you're tuning for each 3 cylinder banks seperately (as in the GTLW) or both combined, 6 cyl, in the crossover (y-pipe) configuration. The resonator is shorter when higher cylinders are combined.

3. Test, test, and retest. I doubt you'll ever get it on the 1st try. R&D costs money!

btw... i'm even more of a hack than Mac. I'm Hack Attack!
 
Dynomax® Performance Mufflers: VT™ Muffler

DynoMax® Performance Exhaust - a leading innovator in performance exhaust technologies - introduced the DynoMax VT™ muffler, a revolutionary, high-flow straight-through stainless steel performance muffler that controls irritating drone while ensuring maximum performance.

DynoMax Valve Technology Mufflers feature an exclusive, precisely calibrated internal valve that redirects exhaust flow, during cruising conditions, to provide Drone-Free Performance™. Hammer the gas and the valve automatically adjusts for maximum exhaust flow, delivering on-demand performance and a deep, throaty drone-free sound.

muf_vt.gif


  • Exclusive Dynomax® Valve Technology.
  • DRONE-FREE Performance™.
  • On-demand performance & sound.
  • Stainless steel construction.
  • Straight-through welded design.
  • Limited Lifetime Warranty.
  • 90 Day Performance Guarantee.
  • (US Patent Pending)

vt_app_chart.jpg


vt_desc.jpg



Anyone hear about the VT?
 
Yeah. I know I'm long-winded, but jeez man... Check out my post #4 of this thread :biggrin:

I think someone (batman, hint, hint) should try them.


Mac Attack said:
Finally, these mufflers have recently come out and look promising. If they had come out back in March when I started this, my outcome may have been totally different. I would like to see someone experiment with these, either in a single configuration like I’ve done, or maybe just a muffler for each exhaust bank:
http://www.dynomax.com/mufflers.php?muffler=vt
Click to expand...
 
BATMANs said:
What I really meant to say, was if u think this design is hog wash. ;)
Click to expand...

I think it would work, but for the first guinea pig, I would recommend merging both exhaust banks together into a 3" pipe, and then only using one muffler to keep cost/weight down. The exit of the muffler could have a pipe that splits and goes to each traditional exhaust exit.

My only question would be longevity and how long that valve would freely open/close before it got gunked up.

Dave

p.s. I haven't done anything on my design as the home, kids, and vacations are occupying all my time. Hopefully I can get this done early next month as I would like to show a finished product to some folks coming to visit.
 
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I wonder how it would sound to just replace the factory mufflers with these.
 
BATMANs said:
What I really meant to say, was if u think this design is hog wash. ;)
Click to expand...
I remember when Mac first posted info about the VT. Due to the lack of images and description I personally cannot figure out how the exhaust gases route once the valve is closed.

DynoMax Valve Technology Mufflers feature an exclusive, precisely calibrated internal valve that redirects exhaust flow, during cruising conditions, to provide Drone-Free Performance™. Hammer the gas and the valve automatically adjusts for maximum exhaust flow, delivering on-demand performance and a deep, throaty drone-free sound.
Click to expand...
In reading the above... I really don't get it. To me, until i'm better informed, I don't see this being more than a gimic, though it should remove the drone just not in an efficient way. For example, it appears the valve is spring loaded not electric or vacuum actuated. The spring rate would have to be so precisely calibrated that at idle it stays partially closed and when full throttle it fully opens? Calibrated to what though? A I4, V6, V8, a NSX, a LSx, a Lambo? Well... the velocity of the gasses passing through each car at "full throttle" varies greatly between cars and is further compounded by different header, intake, heads, FI etc for even that same car... I can't imagine this can ever be a one-size fits all application like they are marketing it to be. Now assuming they did calibrate it to MY CAR then isn't the spring loaded valve a constant hindrance to flow? It seems like it's always fighting to want to stay closed. I don't know... again.. I suffer from small brain syndrome. :confused:

Maybe the premise to my analysis is completely wrong. I'm hoping someone can shed some light on my questions!

btw.. I'm with Mac... I nominate Bats to try it! I know I can be proven wrong. Happens all the time. lol
 
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RYU said:
I remember when Mac first posted info about the VT. Due to the lack of images and description I personally cannot figure out how the exhaust gases route once the valve is closed.


In reading the above... I really don't get it. To me, until i'm better informed, I don't see this being more than a gimic, though it should remove the drone just not in an efficient way. For example, it appears the valve is spring loaded not electric or vacuum actuated. The spring rate would have to be so precisely calibrated that at idle it stays partially closed and when full throttle it fully opens? Calibrated to what though? A I4, V6, V8, a NSX, a LSx, a Lambo? Well... the velocity of the gasses passing through each car at "full throttle" varies greatly between cars and is further compounded by different header, intake, heads, FI etc for even that same car... I can't imagine this can ever be a one-size fits all application like they are marketing it to be. Now assuming they did calibrate it to MY CAR then isn't the spring loaded valve a constant hindrance to flow? It seems like it's always fighting to want to stay closed. I don't know... again.. I suffer from small brain syndrome. :confused:

Maybe the premise to my analysis is completely wrong. I'm hoping someone can shed some light on my questions!

btw.. I'm with Mac... I nominate Bats to try it! I know I can be proven wrong. Happens all the time. lol
Click to expand...

I'm known for making posts with illustrations. The exception is unlike reading the pics of National geographic, people read my words too. :biggrin:

vt_lg.jpg


I just got off the phone with a Dynomax rep and he said that the spring has gone through the equivalent of over a million duty cycles. if it were to fail it would just stay open and that is covered by their lifetime warranty.

The valve staying partially closed redirects the sound waves back to the front of the muffler which eliminates the drone.

At WOT the exhaust gases will force open the flap. The spring pressure is light enough for a weak 4-banger to lift it open.

I might just try this out.

U guys wanna start an R&D fund?

Parts and labor not going to be cheap. I've done this a few times already. :biggrin:

Mac Attack is exempt since pulled his time and resources. Unless if he wants too. :tongue:
 
BATMANs said:
I just got off the phone with a Dynomax rep and he said that the spring has gone through the equivalent of over a million duty cycles. if it were to fail it would just stay open and that is covered by their lifetime warranty.

The valve staying partially closed redirects the sound waves back to the front of the muffler which eliminates the drone.

At WOT the exhaust gases will force open the flap. The spring pressure is light enough for a weak 4-banger to lift it open.

I might just try this out.

U guys wanna start an R&D fund?

Parts and labor not going to be cheap. I've done this a few times already. :biggrin:

Mac Attack is exempt since pulled his time and resources. Unless if he wants too. :tongue:
Click to expand...
Thanks for the info. I still don't buy it but i'm happy to be proven otherwise. The way I see it.. the volume and velocity of gases travelling out of a Civic at say 2000rpm is way different than our LSx at the same rpm. Ok, maybe they'll say... "well, in a V8 application you have to use 2 mufflers to split up the flow" but still... I don't buy the one-size-fits all marketing. I guess they could design it in such a way that it will work just ok for most applications and it might work great if you're lucky and your car is the one that fits in that magic sweet spot the spring is calibrated to... Then again they do claim "Drone-Free Performance™".

If their explanation is right, then if it's light enough to open for a Civic then if I installed one behind my LS1 then it's probably close to fully open at idle. I guess at this point there no sense in bench racing! Try it out Bats! :biggrin:

I've already been working on my prototype behind the scenes with Mac. It's just the issue of time and other priorities right now. It will be a great Fall project though. If my setup does work the design is open for everyone's consumption.

BTW... My friend was helping me transport my NSX last night. He passed me a few times... let's just say I feel in love with the HKS exhaust all over again :) :) :) There's a lot to be said for subtlety but impactful notes.
 
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Just wanted to add that I experienced this first hand this afternoon and its just amazing!
 
Nukem said:
Guess I need to invest in a translater or learn Japaneese
Click to expand...

You can actually run the hyperlink through google and it will translate the page to english.
 

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