Go Back   Home > Forums > General Interest > Everything Else

Everything Else Anything related to audio / video / electronics etc) BUT remember- we have many new forums where your thread may now fit! .... Parts, Equipment & Tools, Construction Tips, Software Tools......

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 29th January 2009, 04:18 PM   #1
diyAudio Member
 
Paradise_Ice's Avatar
 
Join Date: Jun 2004
Location: cosmological consciousness
Default Engine Exhaust tuning Question?

Exhaust builders and tuners claim that the exhaust sound has no influence on the gas velocity, but we know that any pipe can be tuned to match a sound wave, is it possible to tune an exhaust to match the engines exhaust ports sound wave?

What kind of calculations would one need to use?

If this is the sound waves from the engines headers.
Attached Images
File Type: jpg 15_copy.jpg (79.6 KB, 162 views)
  Reply With Quote
Old 29th January 2009, 07:21 PM   #2
diyAudio Member
 
zigzagflux's Avatar
 
Join Date: Oct 2006
Location: Charlotte, NC
This probably doesn't help you very much, but I know the speaker end of Jensen was experimenting with "speaker mufflers" on automobiles about 15 years back. Family member who I don't come into contact with much was working there. Goal was to eliminate traditional mufflers, gaining extra hp output out of the engine while keeping noise levels the same.

Who knows, you might be able to contact someone there who recalls some of the results.
  Reply With Quote
Old 29th January 2009, 10:00 PM   #3
diyAudio Member
 
Paradise_Ice's Avatar
 
Join Date: Jun 2004
Location: cosmological consciousness
Actually that does help, I 'm trying to make an exhaust pipe that has the same resonance as the headers, the idea being to get the lowest impedance in the exhaust, I do not know how Pipe Organ makers or tuners build pipes to vent certain frequencies like 80hz, I am looking to have an exhaust that will resonate at 120Hz 240Hz and 440Hz as these are the main sound waves from my engines headers, I know this sound crazy but I have time and I have never found an acoustically tuned exhaust on a car.
  Reply With Quote
Old 29th January 2009, 10:44 PM   #4
diyAudio Member
 
Join Date: Feb 2004
Location: Queensland Australia
Not crazy at all...."It's the cracked people of the world who let the light in!"

Not quite sure what you have in mind and there may be some confusion about terminology. Are you trying to generate an out of phase resonance that will cancell the existing noise? Or are you looking to reinforce the sound? There is a well developed science of the waves in both exhaust and inlet manifolds. (There are probably entire websites devoted to it.) By exploiting resonances designers can get more gas into and out of a cylinder than would first seem possible. When well done I understand that you can get greater than one atmosphere in the combustion chamber which is a bit "counter intuitive". It is linked with valve timing too and engine spped and only works over a relatively narrow rev' band. That is why they now try to have variable valve timing, variable inlet manifolds etc (Mercedes-Benz sports racers in the 1950'.) The serious texts will sometimes speculate about varyng the length of the exhaust pipe but I can't recall seeing one produced yet. But perhaps you know all this already.....in which case I'm sorry to chat away needlessly.
I am uncertain what you mean by the frequencies generated by the headers...... won't they change as soon as you fit an exhaust pipe to the end of them? Sorry, I'm a little in the dark here but good luck and I hope to learn more.
__________________
"It was the Springtime of the year when aunt is calling to aunt like mastodons bellowing across primeval swamps." P.G. Wodehouse.
  Reply With Quote
Old 29th January 2009, 10:55 PM   #5
kaos is offline kaos  United States
diyAudio Member
 
Join Date: Dec 2005
Location: Los Angeles
This isnít going to help you any, but typically for highest performance the diameter of the pipe is selected based on the cubic inch displacement of the engine (the bigger the engine, the larger the diameter). The operating RPM range determines the optimal length of the pipe, the higher the RPM range the shorter the pipe. This is why you see very short pipes (zoomies) on dragsters. A proper length of pipe results in a reflected rarefaction at the port when the exhaust valve is open during over-lap, maximizing volumetric efficiency. Calculations can be used to get you in the ballpark, but the only way to really find the best combo for a given vehicle is dyno testing. Iíve seen guys actually place restrictions on the end of an exhaust pipe and pick up a few horsepower on the dyno because their exhaust system was too large. Sorry but Iím not enough of a geek to have any formulas for you (so without formulas why am I bothering to post?).
  Reply With Quote
Old 29th January 2009, 11:02 PM   #6
OzMikeH is offline OzMikeH  Australia
diyAudio Member
 
Join Date: Mar 2007
It is done and has been done for years.
It depends if you want maximum performance or maximum volume.

Also if you wish to improve performance at a particular engine speed.

The method I heard of someone using was to paint the exhaust in stripes of heat sensitive paint and run the engine with the exhaust at the desired speed and load on an engine dyno.

The exhaust system was 4 into 1 headers on a V8.

I cant remember if the pipe was cut at temp maximum or minimum, I do know the vehicle could be heard from nearly 20km away in the right weather. The driver and navigator wore earplugs and well padded helmets and still suffered hearing loss for several days.

No idea if the performance advantage.

Another concept is to construct headers with acoustic reflectors in the collector, the idea being to encourage resonance in the pipes to cause a pulse to bounce off the back of the exhaust valve of the next cylinder to open. Such a construction will most likely not fit under a car but would be excellent in a boat. the reinforcement will be most effective at certain engine speeds where you need the boost or if you are going for narrow bandwidth power.

There has been other discussion on here about intake tuning as well, do some searching.
__________________
Help some guys with funny hair bang two rocks together really hard.
http://athome.web.cern.ch/athome/LHCathome/whatis.html
  Reply With Quote
Old 30th January 2009, 03:23 PM   #7
Ron E is offline Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN
Quote:
Originally posted by kaos
Calculations can be used to get you in the ballpark, but the only way to really find the best combo for a given vehicle is dyno testing. Iíve seen guys actually place restrictions on the end of an exhaust pipe and pick up a few horsepower on the dyno because their exhaust system was too large. Sorry but Iím not enough of a geek to have any formulas for you (so without formulas why am I bothering to post?).
Yours is the only really on topic post here, as far as I see. There are sort of competing requirements - least flow restriction requires large diameter, but making a very large pipe will affect low RPM horsepower because flow velocity (inertia) is too low to fully scavenge the charge. So you need to balance the requirements of restriction and minimum flow velocity with length. I am not sure how much of an effect exhaust tuning has, but intake tuning can have a 20% or so effect on volumetric efficiency in a specific narrow RPM range, IIRC. I have seen some dyno runs of different after market exhausts on 4 cylinders and they don't make that much difference, although the best are nearly as good (and as loud) as just taking the muffler off.

Active exhaust systems would probably be used to augment passive systems to reduce low frequency noise, since passive systems are best at the high frequency stuff. it basically works like a noise cancelling headset.
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. óAldous Huxley
  Reply With Quote
Old 31st January 2009, 06:21 PM   #8
diyAudio Member
 
Join Date: Jul 2003
Location: Bath, UK
Good post. Also the 'tuning potential' of exhaust length, based on scavenging, is rather less than the benefits of getting the induction design right (which is also based on tuned lengths and helmholz resonators...)

Something that works against exhaust tuning by length is the high (and variable) temperature of the exhaust gases. This means the effective speed of sound inside the pipe (often 1000-1300m/s) and therefore the 'tuned length' required, varies somewhat. Many performance-orientated manufacturer's exhaust designs incorporate resonators which are actually quite deliberate in decoupling the exhaust length from the powerband; when sized for peak flow, the overall result is quieter, yet flows almost like a short open pipe at the top end ...

Finally, do you really want an engine which has a 'peaky' response ? Two-strokes are the exemplars of the drivability problems that can raise...
  Reply With Quote
Old 31st January 2009, 10:33 PM   #9
diyAudio Member
 
Paradise_Ice's Avatar
 
Join Date: Jun 2004
Location: cosmological consciousness
Thank you for all the responses, the engine in question is turbo charged so the scavenge effect is different from a naturally aspirated engine I think?

The strange thing is the engines main resonance in the headers does not change with an RPM speed increase, it gets louder and quicker for sure, but the 120Hz 240 and 440Hz are are still the main sounds regardless of engine speed, this is what confused me and lead me to ask the question, can I tuned a length of pipe to this wave lengths.

I drove the car with the turbo vented to the atmosphere in the engine bay, no turbo flange cover or down pipe of any sort, this made the turbo spool up very quickly but the actual power was down in the high rpm range, I then weld on a 3 inch down pipe and the longer I made the pipe the more power the engine developed until I connected up the rear back box, it sapped the life from turbo spool up time and dropped the power under boost, I know the silencer function is to reduce sound pressure but it removed so much power in the process, I though there must be a better way.
  Reply With Quote
Old 31st January 2009, 10:47 PM   #10
diyAudio Member
 
Join Date: Jul 2003
Location: Bath, UK
If the engine is turbocharged, the exhaust length has NO bearing at all. All that is required is as low back-pressure as possible, because the turbine is driven by the difference in pressures across it.

I've had a succession of tuned turbo Saabs, amongts othe rtoys, and what seems to work well is a downpipe that expands smoothly from the turbo exhaust flange to a diameter appropriate to the target HP flow (eg 2.5- 3") - hint, smoothly.

After that, the rest of the exhaust system - providing only that it is not actively restrictive in terms of peak flow - has *very* little effect. HTH
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Air Vane RIAA Tuning Question soulmerchant Tubes / Valves 12 28th December 2006 03:37 PM
Tuning Question (Sealed) kiowamec Multi-Way 9 23rd May 2006 07:47 PM
Question about port tuning ostie01 Subwoofers 3 26th September 2005 01:30 AM
testing using HEXFET for exhaust fan Mikka Solid State 2 3rd June 2003 04:12 PM


New To Site? Need Help?

All times are GMT. The time now is 10:41 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2