My new X pipe creation

NSXDreamer2 · 13 May 2010

Hi all, I'm just going to let the pic and videos explaining itself. This is not an easy task:

Car info: stock 91 3.0
tranny: oem 5 sp with comptech 4.55 r&p
exhaust: 13+ year comptech / DC sports / test pipe.

ChadAtlanta · 13 May 2010

I love this type of project. I did something very similar on my G35 coupe. Although they are hard to find, do a google search on a Tornado muffler (iirc) that would fit perfectly. I believe they are out of Australia.

Nice work.

dawk · 13 May 2010

Sounds great!

demigod · 13 May 2010

Sounds fantastic!

RYU · 13 May 2010

I like it.

What tube & muffler diameter did you end up using? Looks like 2 1/2" piping...

What kind of mufflers are those too?

Rusted_nailz · 13 May 2010

Very nice Ferrand! I cant wait to hear it in person one day.

iCEE · 13 May 2010

nice. where do i sign up? :biggrin:

Mac Attack · 13 May 2010

I like it - sounds and looks good!

I run cats for several reasons, but by far prefer the sound without them. Even the shortest cats available are low-pass filters that filter out the higher-pitched "good sounds" ~2000Hz and above.

I'm thinking about redoing my setup with the headers merging together into a single 3.5" pipe and then have an electric cutout where I can bypass a single cat and muffler or not....

Dave

NSXDreamer2 · 13 May 2010

Rusted_nailz said:
Very nice Ferrand! I cant wait to hear it in person one day.

sure Buddy, I would love to check out Wil's exhaust in person and see the difference too..

the muffler are burns, they are serviceable race muffler

piping is 2.25 from cat to top part of the X, then after merge, 2.5 to the muffler.

Yes, the project snow balled and took way more time than we expected, but the end result is pleasing and look at the Scale!!! (16.3 lbs)... We may need to work out some kinks before we roll it into production. With that said, if there's anyone interested in Seattle/Vancouver B.C. area; feel free to PM me.

the biggest draw back right now, is that i have a big dronning noise as the rev climbs from 2000 to 2700 rpm. not a biggie for me as I have the 4.55 final gear, it's quite quick and painless to get through it, and crusing speed at 65mph is already over 3000rpm, which quiets back down and I could carry normal conversation with passenger in car. This could be a problem for a 5 speed NA1 at hwy speed if we just selling the exhaust as-is.

thanks for the compliment guys; please give me more idea and/or suggestions.

Mac Attack · 13 May 2010

NSXDreamer2 said:
the biggest draw back right now, is that i have a big dronning noise as the rev climbs from 2000 to 2700 rpm. not a biggie for me as I have the 4.55 final gear, it's quite quick and painless to get through it, and crusing speed at 65mph is already over 3000rpm, which quiets back down and I could carry normal conversation with passenger in car. This could be a problem for a 5 speed NA1 at hwy speed if we just selling the exhaust as-is.

thanks for the compliment guys; please give me more idea and/or suggestions.

At least you're honest about the drone - I didn't want to ask until someone else brought it up first.

Have you looked at this thread? It might offer some insights on the droning issue:
http://www.nsxprime.com/forums/showthread.php?t=134710

Unfortunately like you said for a 5-speed with a stock rear end, in 5th gear you are in the 2000-2500RPM range from 40-55MPH. That's where a lot of us cruise around in.

You could take a small pipe ~2" in diameter or less, and weld it perpendicular at your x-pipe location. This pipe would point to the front of the car, and then you could fabricate a metal box or capped pipe that could be your Helmholtz resonator tuned to cancel out the 105Hz frequency.

That way, you don't have to run two resonators (one for each bank). While your pipe welded to the crossover would obviously have to be steel, you could make the resonator itself out of aluminum or something like that to keep the weight down. That's what I did.

If I can help, let me know, good luck with the project!

Dave

angus · 13 May 2010

This looks fabulous !

I strayed away from this design due to the drone issue , you could spend some time and try to tune it out as mac says, also the burns mufflers are very nice , they also offer different packing materials so you could try that too.

I really love the look of the angled cannisters!

NSXDreamer2 · 13 May 2010

angus said:
This looks fabulous !

I strayed away from this design due to the drone issue , you could spend some time and try to tune it out as mac says, also the burns mufflers are very nice , they also offer different packing materials so you could try that too.

I really love the look of the angled cannisters!

thanks buddy, your exhaust is an influence of our design, and we chose a different route than yours so we both have our unique product. :biggrin:

AR · 13 May 2010

It looks nice and sounds great, but as long as you used premade thin mufflers you wil have that drone issue.

I had an proto type dual can exhaust and went throught several different mufflers and packaging material density until we hit the right tone. In the end the project was aborted as people here in the UK were not willing to pay £ 650 pounds when they could buy something with a brand name for 3 times the price or in the case of GruppeM 4 times LOL!

BATMANs · 13 May 2010

ChadAtlanta said:
I love this type of project. I did something very similar on my G35 coupe. Although they are hard to find, do a google search on a Tornado muffler (iirc) that would fit perfectly. I believe they are out of Australia.

Nice work.

G35s already sound good stock. I wish my NSX had that sound, well maybe a little louder. But the exhaust pulses sound more like a Ferrari V-6, if they ever made a current model.

What did Nissan do with the exhaust and/or engine for that sound? X-pipe from the factory?

BATMANs · 13 May 2010

AR said:
It looks nice and sounds great, but as long as you used premade thin mufflers you wil have that drone issue.

I had an proto type dual can exhaust and went throught several different mufflers and packaging material density until we hit the right tone. In the end the project was aborted as people here in the UK were not willing to pay £ 650 pounds when they could buy something with a brand name for 3 times the price or in the case of GruppeM 4 times LOL!

I've been running x-pipe for 2 years and have a Moroso Spiral-flow muffler. No packing. It had a deeper sound, but the mufflers do have that 2-3k drone. I was thinking about pulling off the muffler and just running X-pipe and straight pipes after in hope of taking out the drone.

My experience with my GTO and it's X-pipe was that most mufflers (esp. ones that are chambered) seem to either cause or contribute to the drone.

So that had me thinking if I ran no mufflers for the NSX with an X-pipe, then the sound will exhaust out the back instead of bouncing around in the muffler droning.

And yes, alot of "import" car guys, unlike domestic guys, insist on spending 3x for a named brand muffler.

Mac Attack · 13 May 2010

Folks,

Drone is not generated in the mufflers, it is generated by the engine firing rate happening to be at the same resonance frequency inside our cabins.

Unless you have a system in your exhaust piping to cancel out this problem frequency, then you are going to have drone.

The drone frequency is around 100Hz and occurs in a RPM range of 2000-2500. This is a low frequency that requires sufficient muffler volume or length to effectively trap this long wavelength and cancel it out.

If you have short or small mufflers, then the exhaust will drone (unless the mufflers are really, really restrictive like a turbo muffler).

Dave

RYU · 13 May 2010

Mac Attack said:
Folks,

Drone is not generated in the mufflers, it is generated by the engine firing rate happening to be at the same resonance frequency inside our cabins.

Unless you have a system in your exhaust piping to cancel out this problem frequency, then you are going to have drone.

The drone frequency is around 100Hz and occurs in a RPM range of 2000-2500. This is a low frequency that requires sufficient muffler volume or length to effectively trap this long wavelength and cancel it out.

If you have short or small mufflers, then the exhaust will drone (unless the mufflers are really, really restrictive like a turbo muffler).

Dave

Dave - in addition, shouldn't 2.25" mufflers further attenuate drone vs the 2.5" mufflers used here?

... this was the purpose of my question above.

nsxlife · 14 May 2010

LOVE IT!!!

Thanks for letting me drive it and check it out today Ferrand! Your setup is a little loud for me, but maybe with my high flow cats it'll tone it down some!?

Sign me up brother.

angus · 14 May 2010

Mac Attack said:
Folks,

The drone frequency is around 100Hz and occurs in a RPM range of 2000-2500. This is a low frequency that requires sufficient muffler volume or length to effectively trap this long wavelength and cancel it out.

Dave

Isn't a 100hz wavelength about 10ft long @ room temp?

Mac Attack · 14 May 2010

ryu said:
Dave - in addition, shouldn't 2.25" mufflers further attenuate drone vs the 2.5" mufflers used here?

... this was the purpose of my question above.

Definitely. The more exhaust restriction you have (smaller diameter piping), the more it will attenuate the sound overall from the engine. Then, the problem exhaust frequency (105Hz) will have a lower amplitude to interact with the structural resonance in our vehicles and make it just a tad quieter.

You'll still have an annoying resonance, even if you used 2" diameter. Keep in mind, the smaller you go, the more restrictive and less performance you get then.

That's why to have a high performance exhaust that doesn't hinder the flow and doesn't drone, you need to have some kind of resonance chamber connected.

angus said:
Isn't a 100hz wavelength about 10ft long @ room temp?

Yes, but for exhaust, you have to know what the speed of sound is in hot exhaust gases. This is from the other thread I linked to earlier on how a quarter wave resonator works on mine:

If the side branch tube is sized correctly, the reflected wave leaving the capped side branch will be 180degrees out of phase by the time it goes back to the branch - therefore canceling that frequency out.

The formula to calculate the length is:

L = v / 4f, where

L = Length of capped side branch in feet
v = speed of sound in exhaust gas (feet/second)
f = your desired frequency to reduce

So, you need to know your problem frequency first.

A quick online search said speed of sound in exhaust gas was ~1150 ft/sec. I back-calculated 1250 ft/sec after everything was done. This is a function of exhaust temperature. As there is no exhaust flowing through this bypass, it stays pretty cool (I can touch the capped end after hard driving with no burning). So, go with 1250 ft/sec starting out.

The factor of 4 is due to it being a quarter-wave resonator ....

So, let's say you have a problem frequncy of 105Hz at ~2k RPM.

Your capped side branch length should be:

L = 1250 / (4*105) = 3 feet.

There's a little more to it.... Your side branch should be the same diameter as the exhaust pipe for maximum sound reduction. Mine's not since I didn't want to totally elliminate the 100Hz frequency. Engine firing rate is what gives an exhaust a powerful sound. My 2.25" side branch got rid of my resonance problem, so I didn't feel the need to go any larger. I could go smaller to save weight, but that's for the future....

Also, to attenuate a wider frequency range (but not as effectively cancel those frequencies), you can stuff steel wool in the end of the side branch. Kinda like stuffing filler in speaker boxes to make them "appear" larger.

Dave

EdinKali · 14 May 2010

If you can cancel out that drone and sell it for a reasonable price you will sell a ton of them. Definitely sexy looking and light to boot.

RYU · 14 May 2010

Mac Attack said:
Definitely. The more exhaust restriction you have (smaller diameter piping), the more it will attenuate the sound overall from the engine. Then, the problem exhaust frequency (105Hz) will have a lower amplitude to interact with the structural resonance in our vehicles and make it just a tad quieter.

You'll still have an annoying resonance, even if you used 2" diameter. Keep in mind, the smaller you go, the more restrictive and less performance you get then.

That's why to have a high performance exhaust that doesn't hinder the flow and doesn't drone, you need to have some kind of resonance chamber connected.

Dave

I hate to bastardize this beautiful exhaust but this exhaust theory stuff is really interesting to me.

I hope i'm not going off topic here. Just trying to find options to eliminate the drone. What do you think of these two options? Forgive the crappy illustration.

Could you use a resonated chamber to cancel out the ~100hz drone this way? I'm thinking along the lines of a Helmholz (sp?) resonator.

What I don't know if it will be more effective with a block in the middle making each chamber truly isolated.

Unfortunately, this will probably add another ~3-5lbs. It's now starting to look like a pretzel exhaust

Mac Attack · 15 May 2010

The first pic might do it :smile:.... I would start with a 36" long pipe at least 2" in diameter connecting the two banks and see if that works. It shouldn't add more than 2lbs and would be well worth it to eliminate the droning.

In the second pic, I don't think you have enough space for a 36" long pipe for each bank.

Good ideas!

Dave

ryu said:
I hate to bastardize this beautiful exhaust but this exhaust theory stuff is really interesting to me.

I hope i'm not going off topic here. Just trying to find options to eliminate the drone. What do you think of these two options? Forgive the crappy illustration.

Could you use a resonated chamber to cancel out the ~100hz drone this way? I'm thinking along the lines of a Helmholz (sp?) resonator.

Unfortunately, this will probably add another ~3-5lbs. It's now starting to look like a pretzel exhaust

Jack Sparrow · 15 May 2010

The sound is amazing. Would this setup work for a turbo car or do all turbo NSX's have custom exhaust setups depending upon the kit?

angus · 15 May 2010

It might be cool to install an exhaust valve in the "X"

My new X pipe creation

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