View Full Version : Helmholtz Resonance exhaust

04-13-2010, 11:56 PM
After reading this months Fact or Fiction topic on Helmholtz Resonance exhaust in Import Tuner , I'm pretty intrigued. After a little researching, it appears the technology is more often discussed with intake manifolds than anything, but is this the wheel reinvented?

The gist is this : "Exhaust gasses are blown across built in resonance chambers, and the frequency of pressure waves created therein pushes exhaust gas through the tubing and out into the atmosphere"

Dynojet Numbers with a 2007 nissan 350Z (VQ35DE Rev-Up Engine)

Stock Exhaust : 225.7 WHP 207 LB-FT
Motordyne ART Test Pipes & Shockwave V2 Catback : 257.3 WHP 238.8. LB-FT

The science appears pretty solid, but to what power level does it remain effective and gains remain to be seen?




04-14-2010, 10:37 AM
Actually they are using the Helmholtz Resonance terminology but from all my research before it has to do with resonate frequencies created from vacuum draw, there is an actual term for the scavenging practice, using the negative event behind the pressure pulse wave in exhaust. Helmholtz theory was that if the airflow got to a specific speed its would actually accelerate and gain energy and that all tubes have said frequency that they achieve this phenomenon.
Junk science terminology rehash.
Big trick with exhaust is to size it properly and have the cylinder pulses pull each other out as the engine runs, this is called scavenging cycle according to my knowledge. This is one of several reasons X and H pipes help and like the old Flowmaster Force II Scavenger Collectors I have for my big block headers.

04-16-2010, 04:19 AM
Also, tuning the length of your primary tubes helps a lot with scavenging, you not only want them at the exact same length, you need that length to be in tune with the size and firing order of the engine and when equal length isn't possible, the tubes can be a higher multiple of the correct length in order to retain the frequency.

04-16-2010, 07:39 PM
The only place I've seen something like that is on a Renault LeCar that I had once upon a time. It had a pipe that branched off the exhaust at about the back of the door, ran out and forward to about the front of the rocker panel. With a 4 speed transmission that car wasn't a natural highway cruiser to say the least. The day it blew out that "branch line" exhaust pipe near the beginning of a 150mi Interstate trip I thought my head was going to explode.

04-25-2010, 06:58 AM
Big trick with exhaust is to size it properly and have the cylinder pulses pull each other out as the engine runs, this is called scavenging cycle according to my knowledge Mind you, I'm a novice when it comes to this, but this is what i gather so far in terms of exhaust. It starts at the headers and ends at the tip? If your going to build a custom exhaust manifold tailored to your engines characteristics (N/A, Turbo, Supercharged, type of cam, RPM, Power-band, Etc.), and As ArtosDracon stated, you size each Primary in diameter, length, and shape to accommodate all said characteristics. Then extend that to the collector type, and then down through the rest of the exhaust. True duels, X-Pipe, or H-pipe. All of this can be designed to make power in the RPM range you need it. Up, down, or anywhere in-between. If all of this can be tuned to aid in scavenging and optimum pulse, can't this as well? Exhaust design and it's effects on performance, mainly because it's effects are completely dependent on design, is fascinating. The engine is gonna do what it does, but being able to tune it, albeit mildly, off the waste it produces is pretty interesting. It may not make a noticeable difference on a 500 HP engine, but what about on an engine with more conservative numbers?

If the exhaust has been completely optimized for the engine, could this not noticeably contribute by accelerating the pulse?? The phenomenon looks pretty legit, but does this fall int the same category as Fuel line magnets?

I suppose I equate this idea to the little scoop McLaren added to their F1 car this season, nothing mechanical about it. A new idea that shows a noticible gain in performance. Apples to Oranges maybe, but in the same context I think.

04-28-2010, 07:21 PM
Trying to engineer a 180 degree header pulse... Seems like this to me

05-05-2010, 05:34 PM
also take note that the test was done with stock pipes Vs. this aftermarket setup. Larger tubes, mufflers with less restriction, better bends could be responsible for the gain.

I would prefer to see it with identical systems with the only difference being the chambers.

Apples to apples?

05-06-2010, 10:26 PM
The full article is now online. They do it on the 2007 Nissan 350Z and the Test pipe shows 11.2 HP and 29.7 LB-FT over the comparable aftermarket test pipe.


05-19-2010, 11:10 AM
ok look at it this way, exhaust doesnt accelerate as it cools, this is why the exhaust manufacturers try to use each pulse to pull, and hence push each next pulse out, see each time a valve opens the hot gasses are pushed out, but if engine is running then the dynamics are to use the energy t opull other out, making pressure pulses and behind each as it leave is a negative pressure event, thus pulling air out of exhaust.IE pressure higher pops out of pipe, atmosphere is lower so it tries to pull exhaust out.
Helmholts theory is the acceleration of the air to a point where it has enough energy in speed to maintain or accelerate rather than having engine pull it in. Something like once a plane gets over sound barrier it goes much faster with less power input.
Think of it this way, someone pulls out a $500 word, throws it on a new exhaust and some people buy it, and they make money.
Learn thermal dynamics an fluid dynamics and you will get more out of it than Helmholts theory.
Which by nature works more on the intake, supposedly old school ram tubes are a user of this effect, it has to d owith the mass of the air/fuel charge going so fast its mass starts to accelerate on its own. With pressure pulse waves, and heat Ill stick with know factors and some better design techniques.
As for those increases you will see similar changes as the mix of parts change too.
2 350 Chevy engines, larger tube headers on one and smaller on the other,,, the came the old .453/.474 268/274 design, everything other than headers is same, small header engine makes better power, large tube loses on bottom end big time. take same engines and put big ol .600/.600 298/298 cam in and guess what, big header setup will win more points . This is assuming engines built to match cam designs

05-19-2010, 08:18 PM
Consensus is snake oil I see. Doesn't help that it's adopted by no major exhaust manufacturers. Lot's of good info :cheers:

CurtiSS 69
05-30-2010, 03:59 PM
Sound resonance cavity tuning in exhaust systems is not "Snake Oil". You can read about experiments conducted by folk's on the Phd level in this book: The Scientific Design of Exhaust and Intake Systems (Bentley Publishers), Trade paperback (2003)
by Philip Hubert Smith, John C Morrison, Phillip H Smith. They had no commercial gains from their experiments -it wasn't done to boost a product- but to make break throughs in the science and publish the results. There are two different phenomia occur here: Pressure Wave tunning which is common knowledge and Acoustic Wave tuning which isn't well known. Pressure Wave tuning mentioned by others above: The proper length and diameter tubing will deliver a low pressure reflection to aid exhaust scavenging . A low pressure reflection to aid exhaust scavenging can also be created with sound resonnace chamber as well. It works like a tuning fork
http://www.physicsclassroom.com/class/sound/u11l1c.cfm (http://www.physicsclassroom.com/class/sound/u11l1c.cfm) and will also produce a low pressure reflection as well. Of course with both phenomia the low pressure reflections are only during certain frequency ranges (i.e. tuned header pipes work at specific rpms and work against at others).

The question should be asked why isn't anyone using this technology? I can think of several reasons: Space, bulk, and heat generation. Service issues due to this vibrating "organ pipe" rattling things loose. The gains aren't huge and only occur at certain rpm ranges. As an example remember Chysler's Ram Induction Tuning in the early 60's. That seemed like a good idea as well. Even though it worked the disbenefits out weighed the benefits. Hemholtz cavities fall into a similar catagory.


CurtiSS 69

06-11-2010, 03:00 PM
one would think a properly designed "shorty" header would scavange better than a long tube... I still want to someday have a street car with 180 deg headers. If not for the scavanging... then the sound... :D

08-30-2010, 11:40 AM
The Nissan article is interesting... if you read the whole thing.

IMHO, I think it's more a case of controlling noise. Manufacturers us those chambers on intake pipes to quiet the howl from the intake.

The principle is explained well here:

It's for real, and is worth a look! I bet these could be tunned vs. rpm, if the chamber volume could be varied in conjunction w/ rpm. Cool stuff...

09-29-2010, 05:21 PM
This has been around for years. I remember some mustang guys experimented with it as an improvement on the "drone" at highway speeds. I think the reason most major manufacturers don't use it is cost(engineering costs). The testing requires a specifically tuned cavity that is specific to the engine type, firing order, pipe diameter, other mods and rpm specific. Its definitely something I want to try on the wagon when the time comes to tuned the exhaust to be drone free as highway speeds.

10-31-2010, 05:04 PM
Many of the import exhaust tuners add those extensions off the pipe just after the headder collector to reduce, if not eliminate, droning from the fart can exhausts. I have a Honda S2000 and belong to a S2000 club. Many members have these crazy, and expensive, exhasts on their cars. Those without the pipe arre almost unbearable at low rpm cruise. Those with it is a marked improvement. There is no discernable powergain though.

11-04-2010, 08:21 AM

Does GM qualify as a major exhaust manufacturer? I saw this on the camaro5 board, and it is from a new camaro. Apparently they have a drone problem, that is made worse by the DOD in the automatic cars.

It works.

11-20-2010, 07:23 PM
there is no savaging gain to be had by J tubes. savaging happens in the header. however noise cancleation can be achieved anywhere along the path.

every manufacture uses this technique to cancel out noises on the intake and exhaust. they have been doing it since 1980 or so. the mathematics behind it are not difficult. you can actually make your own J tubes with NO calculations with just a little trial and error. the 'technology' is very old as it is based on basic acoustics which has not changed in almost a century. anyone who makes their own loudspeaker enclosures will instantly recognize this as old hat... it's just tuned vents. in most audiophile applications the vents are tuned to a desired Hz to amplify the effects of a subwoofer. in this application the goal is to tune the Hz away from the natural resonance Hz so that cruising drone isn't so annoying. audio guys do this as well... audiophile grade tweeters are tuned to cancel out their natural resonance Hz to achieve flat response.

If you want to do some reading, Vance Dickason is the Pozzi/Prodigy/DSE of loudspeaker design, google him to find his books. partsexpress.com has a forum that might be useful as well.

properly designed, even the nastiest of cams can be OEM silent with a resonator, J tube and muffler.