Active NSX Exhaust System
- Thread starter Mac Attack
- Start date
Thanks, all this recent talk on F1 sound has gotten me enthused on completing Version3!
Just began the dismantling....
Planned improvements of Version3:
-Tuned aluminum "drone eliminator" resonator for both quiet and loud modes (instead of just quiet mode like Version2)
-Quieter quiet mode
-Reduced rasp in loud mode
-Improved aesthetics as it will tuck back in more and have four exhaust tips
-Hopefully have some resonant tuning to amplify some desired high-pitch frequencies
-All this with no weight increase over Version2 (21 lbs with cat)
Just began the dismantling....
Planned improvements of Version3:
-Tuned aluminum "drone eliminator" resonator for both quiet and loud modes (instead of just quiet mode like Version2)
-Quieter quiet mode
-Reduced rasp in loud mode
-Improved aesthetics as it will tuck back in more and have four exhaust tips
-Hopefully have some resonant tuning to amplify some desired high-pitch frequencies
-All this with no weight increase over Version2 (21 lbs with cat)
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All looks great, but your clips aren't working!
Thank you.
I must have accidentally deleted some of the clips from my Vimeo account. Hopefully I'll get some new ones up shortly!
Well, I started cutting my tailpipes. The four lengths are 19.5", 16.5", 14", and 12". No, they won't be sticking out varying distances from the rear! I've got something cool worked up :wink: Remember, the Lexus LFA has three tailpipes - each length is tuned to a unique frequency as well :wink:
If the excitation frequency is high enough, I should get a 10db increase in volume at the highlighted frequencies below. They are color-coded, as each tailpipe length will resonate and amplify a specific frequency. Depending if it's a 2nd or 3rd harmonic from the primary engine firing rate, the resonators should cover a broad range of engine RPM.
I must admit this might sound a little strange as it's accelerating, because first at lower RPM's (~2100 to ~3700 RPM), the pitch should increase with RPM as the 3rd harmonics are amplified.
Then, from ~3200 to ~5400RPM, the pitch will drop back down and rise again as the 2nd harmonics are amplified.
I'm predicting that 3500RPM should sound really sweet because I'll have both ~350 and ~525Hz at the same time.
We'll see :redface:
Dave
I must have accidentally deleted some of the clips from my Vimeo account. Hopefully I'll get some new ones up shortly!
Well, I started cutting my tailpipes. The four lengths are 19.5", 16.5", 14", and 12". No, they won't be sticking out varying distances from the rear! I've got something cool worked up :wink: Remember, the Lexus LFA has three tailpipes - each length is tuned to a unique frequency as well :wink:
If the excitation frequency is high enough, I should get a 10db increase in volume at the highlighted frequencies below. They are color-coded, as each tailpipe length will resonate and amplify a specific frequency. Depending if it's a 2nd or 3rd harmonic from the primary engine firing rate, the resonators should cover a broad range of engine RPM.
I must admit this might sound a little strange as it's accelerating, because first at lower RPM's (~2100 to ~3700 RPM), the pitch should increase with RPM as the 3rd harmonics are amplified.
Then, from ~3200 to ~5400RPM, the pitch will drop back down and rise again as the 2nd harmonics are amplified.
I'm predicting that 3500RPM should sound really sweet because I'll have both ~350 and ~525Hz at the same time.
We'll see :redface:
Dave
i applaud your attempt to apply scientific principles in your project instead of 'shooting from the hip' while hoping for a reasonable outcome.
Thanks - I went in stages as I wasn't smart enough to do this all at once!
To briefly summarize:
Stage 1) My first attempt at the lightest, freest flowing system I could get. This actually required some thought to lay everything out with equal losses between both heads. I quickly realized the drone was unbearable and put in a tuned resonator to eliminate the problem frequency.
Stage 2) My second attempt was to sacrifice a little weight to have the ability to go from loud-all-the-time, to a switchable mode via an electric cutout that would quiet the exhaust for 75% of my driving around town.
Stage 3) Hopefully my 3rd and final attempt to improve Stage 2 for sound quality.
We'll see
Would you mind sharing a little more on what you did please AR?
Dave
To briefly summarize:
Stage 1) My first attempt at the lightest, freest flowing system I could get. This actually required some thought to lay everything out with equal losses between both heads. I quickly realized the drone was unbearable and put in a tuned resonator to eliminate the problem frequency.
Stage 2) My second attempt was to sacrifice a little weight to have the ability to go from loud-all-the-time, to a switchable mode via an electric cutout that would quiet the exhaust for 75% of my driving around town.
Stage 3) Hopefully my 3rd and final attempt to improve Stage 2 for sound quality.
We'll see
Would you mind sharing a little more on what you did please AR?
Dave
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what are those?
Patriot Exhaust Varaflow SFI Mufflers
Only comes in 2.25" perforated core so I would have to run two. If they had this in a 3" opening i'd try it.
Been sick the past 1.5 weeks, but here's a little progress....
The only stuff I'll be able to use from the old system is from the headers to the merge.
The only stuff I'll be able to use from the old system is from the headers to the merge.
Any updates Mac? :smile:
Sadly, not much on the exhaust.
I've been getting all my other little projects out of the way... doing paint work (touch-up, paint correction, painting wheels, retouching calipers), cleaning random bits (like removing the front end), changing engine/transmission oil, etc.
I did manage to get the little exhaust tailpipes cut to length, and get my 3" piping all welded up. Now I need to weld on the tailpipes. The aluminum resonator will have a band clamp to the steel section.
The butterfly valve will go between the two flanges on the 3" pipe sections below.
The 2.25" cat will be added as shown.
My weekend calendar is still clear - maybe I can get it finished then :redface:
Dave
I've been getting all my other little projects out of the way... doing paint work (touch-up, paint correction, painting wheels, retouching calipers), cleaning random bits (like removing the front end), changing engine/transmission oil, etc.
I did manage to get the little exhaust tailpipes cut to length, and get my 3" piping all welded up. Now I need to weld on the tailpipes. The aluminum resonator will have a band clamp to the steel section.
The butterfly valve will go between the two flanges on the 3" pipe sections below.
The 2.25" cat will be added as shown.
My weekend calendar is still clear - maybe I can get it finished then :redface:
Dave
Got the loud part done, now I need to weld in the cat.
It's still too early to tell if the resonance tuning worked because it's so freaking loud, but enjoy a quick rev:
<iframe src="http://player.vimeo.com/video/16617042" width="400" height="300" frameborder="0"></iframe><p><a href="http://vimeo.com/16617042">Untitled</a> from <a href="http://vimeo.com/user1744194">Dave</a> on <a href="http://vimeo.com">Vimeo</a>.</p>
A shot underneath - After the cat gets welded in, I'll get this all cleaned and painted. Also, I need to rotate the valve gearbox/motor out of the way:
The exhaust pipes are numerous, small in diameter, and hang down low so that the exhaust can "activate" this portion of my diffusor for more downforce. I'm surprised it all lined up in the end :tongue:
It's still too early to tell if the resonance tuning worked because it's so freaking loud, but enjoy a quick rev:
<iframe src="http://player.vimeo.com/video/16617042" width="400" height="300" frameborder="0"></iframe><p><a href="http://vimeo.com/16617042">Untitled</a> from <a href="http://vimeo.com/user1744194">Dave</a> on <a href="http://vimeo.com">Vimeo</a>.</p>
A shot underneath - After the cat gets welded in, I'll get this all cleaned and painted. Also, I need to rotate the valve gearbox/motor out of the way:
The exhaust pipes are numerous, small in diameter, and hang down low so that the exhaust can "activate" this portion of my diffusor for more downforce. I'm surprised it all lined up in the end :tongue:
It's amazing how much volume comes out of those 4 small pipes! I also noticed that almost all of the low end noises have been filtered out. It's especially prevalent at idle. Can't wait to hear what 'quiet mode' will sound like!
That's funny - the low frequencies are still there (I played it through my headphones at work to confirm). It still sounds like a musclecar below 3500RPM's, and then all hell seems to break loose.
Yeah, I'm excited about the quiet mode too now. I've got Friday off if I can convince my wife to watch the kids just a bit more :redface:
Dave
You know I just played it thru my headphones and not my crappy monitor speakers. You're right.. the lows are still there but still a bit more attenuated than your prev versions i'd say.
- Joined
- 19 February 2008
- Messages
- 1,532
MAC -
Hats off to you so far man... when your final design is done... hit me up for a location to grab some better materials if your interested
Regards
Hats off to you so far man... when your final design is done... hit me up for a location to grab some better materials if your interested
Regards
Hey, thanks!
The craftsmanship of your systems are amazing - have you considered aluminum for some portions to save even more weight? I know it has it's drawbacks, but if you put in some stress relief stainless flex sections, and clamp onto the aluminum portion, I think you could get a reallllly light and even more unique system.
Mine's getting up there in weight now. I'll weigh it when the cats welded on.
Dave
The craftsmanship of your systems are amazing - have you considered aluminum for some portions to save even more weight? I know it has it's drawbacks, but if you put in some stress relief stainless flex sections, and clamp onto the aluminum portion, I think you could get a reallllly light and even more unique system.
Mine's getting up there in weight now. I'll weigh it when the cats welded on.
Dave
- Joined
- 19 February 2008
- Messages
- 1,532
Thanks Dave...
We have an almost 100% aluminum downpipe on an rb swaped s13...
We have been using aluminum with v-bands on custom exhausts. There is a weight savings... but we cant sell them in aluminum... aluminum just cant handle the heat over the long term.. even with flex sections... they break over time.
Good job once again....
I understand about the heat and stress.
I just brought one of these bad-boy $15k thermography scanners home from work to play with:
I'll post some pics of the heated cat and muffler soon. Because of the space limitations, I already tried to get some of the headers and it was washed out by the engine signature :frown:
I want to get some temperature profiles of the tires and the front end after some high speed runs too.
Dave
I just brought one of these bad-boy $15k thermography scanners home from work to play with:
I'll post some pics of the heated cat and muffler soon. Because of the space limitations, I already tried to get some of the headers and it was washed out by the engine signature :frown:
I want to get some temperature profiles of the tires and the front end after some high speed runs too.
Dave
sweet.
It's finished 
Final weight is exactly 25 pounds, but that's with the valve and catalytic convertor. Not bad really for a free-flowing 3" straight-through system, but also with the option for a quiet system when wanted.
Oh, and no droning whatsoever :biggrin:
It sounds incredible fully opened up.
The "Quiet Mode" has two separate vortex shedding frequency generators to give it a unique sound, just downstream of the cat inside of the 2.25" piping.
Dave
Final weight is exactly 25 pounds, but that's with the valve and catalytic convertor. Not bad really for a free-flowing 3" straight-through system, but also with the option for a quiet system when wanted.
Oh, and no droning whatsoever :biggrin:
It sounds incredible fully opened up.
The "Quiet Mode" has two separate vortex shedding frequency generators to give it a unique sound, just downstream of the cat inside of the 2.25" piping.
Dave
Excellent work Dave..can't wait to see the final results on vid!
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