Exhausts - Universal Threads

[amandeepkamboj19]

MAN O MAN how did i missed this thread guys i have lot of info regarding exhaust.
I collected this info because i am designing exhaust for my bike

I dont know if i can post this much in a single post but i am still posting it.


Exhaust Muffler Design Principles

Basic Concepts
Internal combustion engines are typically equipped with an exhaust muffler to suppress the acoustic pulse generated by the combustion process. A high intensity pressure wave generated by combustion in the engine cylinder propagates along the exhaust pipe and radiates from the exhaust pipe termination. The pulse repeats at the firing frequency of the engine which is defined by f=(engine rpm x number of cylinders)/120 for a four stroke engine. The frequency content of exhaust noise is dominated by a pulse at the firing frequency, but it also has a broadband component to its spectrum which extends to higher frequencies. Measurements of the exhaust pipe pressure pulse on a Continental O-200 engine [4] show that the majority of the pulse energy lies in the frequency range of 0-600 Hz. Exhaust mufflers are designed to reduce sound levels at these frequencies.
In general, sound waves propagating along a pipe can be attenuated using either a dissipative or a reactive muffler. A dissipative muffler uses sound absorbing material to take energy out of the acoustic motion in the wave, as it propagates through the muffler. Reactive silencers, which are commonly used in automotive applications, reflect the sound waves back towards the source and prevent sound from being transmitted along the pipe. Reactive silencer design is based either on the principle of a Helmholtz resonator or an expansion chamber, and requires the use of acoustic transmission line theory.
In a Helmholtz resonator design a cavity is attached to the exhaust pipe. At a specific frequency the cavity will resonate and the waves in the exhaust pipe are reflected back towards the source. However there are also pass band frequencies where the resonator has no effect and so resonator muffler design is targeted to specific frequencies where the majority of the attenuation is required. In some designs, the muffler has several resonators of different sizes to target a range of frequencies.Expansion chamber mufflers reflect waves by introducing a sudden change in cross sectional area in the pipe. They do not have the high attenuation of the Hemholtz resonator, but have a broadband frequency characteristic, with pass bands when half the acoustic wavelength equals the cavity length. Their performance also deteriorates at higher frequencies when the cross axis dimension of the muffler is 82% of the acoustic wavelength (Davis, Stokes, Moore and Stevens [5]). Some expansion chamber muffler systems are also packed with sound absorbing material which helps to improve the high frequency attenuation.
In all muffler designs the tailpipe length can have an important effect. The tailpipe itself acts as a resonant cavity that couples with the muffler cavity. The attenuation characteristics of a muffler are modified if the design tailpipe is not used. Also, the effect of exhaust gas flow speed has a detrimental effect on the muffler performance. Beranek[6] gives examples in which the muffler attenuation is reduced from 35 dB to 6-10dB when the flow speed is increased from zero to 230 ft/sec. In typical industrial or diesel truck engine applications the exhaust flow speed can be 164 ft/sec to 390 ft/sec [6]. The effect of flow is related to the interaction of sound with turbulence and will be dependent on the internal design of the muffler.

[amandeepkamboj19]

Design Procedures
Design procedures for resonator mufflers are given in Beranek [6] and Bies and Hansen [7], but the process is complex. The procedure is to specify the resonant frequency of the muffler and the desired attenuation. A cavity volume is calculated and then the area of the openings (or connectors) between the exhaust pipe and the cavity must be calculated. Finally a wire or cloth screen to cover the openings must be chosen with the correct flow resistance to provide the correct damping (this reduces the maximum attenuation, but helps to reduce the effect of the pass bands where no insertion loss is achieved). Introducing tailpipes can significantly improve the muffler performance and more detailed consideration of acoustic transmission line theory [5,7] is required to properly design the tailpipe.

Typical Muffler Designs

[amandeepkamboj19]

some images

[amandeepkamboj19]

this is just a bit of it i have lot more info on exhaust

one more thing i really want to post this one
Exhaust backpressure the myth

I. Introduction
One of the most misunderstood concepts in exhaust theory is backpressure. People love to talk about backpressure on message boards with no real understanding of what it is and what it's consequences are. I'm sure many of you have heard or read the phrase "[COLOR=#22229C ! important][COLOR=#22229C ! important]Engines[/COLOR][/COLOR] need backpressure" when discussing exhaust upgrades. That phrase is in fact completely inaccurate and a wholly misguided notion.

II. Some basic exhaust theory
Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficently. Exhaust gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4 cylinder [COLOR=#22229C ! important][COLOR=#22229C ! important]motor[/COLOR][/COLOR] will have 4 distinct pulses per complete engine cycle, a 6 cylinder has 6 pules and so on. The more pulses that are produced, the more continuous the exhaust flow. Backpressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream.

III. Backpressure and velocity
Some people operate under the misguided notion that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It's not hard to see how this misconception is appealing - wider pipes have the capability to flow more than narrower pipes. So if they have the ability to flow more, why isn't "wider is better" a good rule of thumb for exhaust upgrading? In a word - VELOCITY. I'm sure that all of you have at one time used a garden hose w/o a spray nozzle on it. If you let the water just run unrestricted out of the house it flows at a rather slow rate. However, if you take your finger and cover part of the opening, the water will flow out at a much much faster rate.

The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be traveling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you want make sure the pipe is wide enough so that there is as little backpressure as possible while maintaining suitable exhaust [COLOR=#22229C ! important][COLOR=#22229C ! important]gas[/COLOR][/COLOR] velocity. Backpressure in it's most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust flows backwards, which is not good. The trick is to have a pipe that that is as narrow as possible while having as close to zero backpressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters are best suited to a particular RPM range. A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of backpressure at high rpm. Thus if your powerband is located 2-3000 RPM you'd want a narrower pipe than if your powerband is located at 8-9000RPM.

Many engineers try to work around the RPM specific nature of pipe diameters by using setups that are capable of creating a similar effect as a change in pipe diameter on the fly. The most advanced is Ferrari's which consists of two exhaust paths after the header - at low RPM only one path is open to maintain exhaust velocity, but as RPM climbs and exhaust volume increases, the second path is opened to curb backpressure - since there is greater exhaust volume there is no loss in flow velocity. [COLOR=#22229C ! important][COLOR=#22229C ! important]BMW[/COLOR][/COLOR] and Nissan use a simpler and less effective method - there is a single exhaust path to the muffler; the muffler has two paths; one path is closed at low RPM but both are open at high RPM.

IV. So how did this myth come to be?
I often wonder how the myth "Engines need backpressure" came to be. Mostly I believe it is a misunderstanding of what is going on with the exhaust stream as pipe diameters change. For instance, someone with a civic decides he's going to uprade his exhaust with a 3" diameter piping. Once it's installed the owner notices that he seems to have lost a good bit of power throughout the powerband. He makes the connections in the following manner: "My wider exhaust eliminated all backpressure but I lost power, therefore the motor must need some backpressure in order to make power." What he did not realize is that he killed off all his flow velocity by using such a ridiculously wide pipe. It would have been possible for him to achieve close to zero backpressure with a much narrower pipe - in that way he would not have lost all his flow velocity.

V. So why is exhaust velocity so important?
The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The guiding principles of exhaust pulse scavenging are a bit beyond the scope of this doc but the general idea is a fast moving pulse creates a low pressure area behind it. This low pressure area acts as a vacuum and draws along the air behind it. A similar example would be a vehicle traveling at a high rate of speed on a dusty road. There is a low pressure area immediately behind the moving vehicle - dust particles get sucked into this low pressure area causing it to collect on the back of the vehicle. This effect is most noticeable on vans and hatchbacks which tend to create large trailing low pressure areas - giving rise to the numerous "wash me please" messages written in the thickly collected dust on the rear door(s).



source-http://www.thumpertalk.com/forum/showthread.php?t=659727

Some say that "an engine needs backpressure to work correctly." Is this true?

No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.
The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.
The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.
The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.
Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.
Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.


source-http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm

[aaron]

thanks baba for the information...... other than just uploading pics like some guys....

[viv.nomad]

hii guys....

it s abt exhaust modification of bike unicorn . well i dont need tuned one ... i just want to get some opinions abt and idea which is just bulbed in my mind..

so guys what if i crop the 8" portion of muffler .. what improvement I'll see...

any body who tried such mod or want to do so can pm me.. we can have some talk\chat...

pic for this idea...

from this


to this ..




what will be the effect on sound and is this mod worth it ...

[kb100]

You cant just chop off ur exhaust like that and expect performance increase... however if u manage to remove one of the baffle plates inside the uni's muffler there might be a slight chance of performance increase and an increase in sound.

[revtech]

can the people who have these FFE post a video with the sound.

[viv.nomad]

where to get perforated tube guys ..... need it for some mod ..

need 30 mm perforated tube of length 12"...

and where one can get the straight pipe bent into a smooth angled shape ...

[jas_mirage]

changing the silencer of my Pulsar 180 Dtsi

Just some days back, the silencer end cap of my bike decided to commit suicide by jumping of a bridge while I was riding (Still cant figure out how the end cap came loose).

So now I have to change the silencer. I was thinking that it would be a gud opportunity to go in for a mod at this stage. Now let me see has anyone attempted putting the silencer of the FZ16 on th pulsar?

Can anyone suggest something for the same?

[viv.nomad]

some body also tell me what is this "exh valve opening in degrees BBDC" for unicorn !

Just some days back, the silencer end cap of my bike decided to commit suicide by jumping of a bridge while I was riding (Still cant figure out how the end cap came loose).

So now I have to change the silencer. I was thinking that it would be a gud opportunity to go in for a mod at this stage. Now let me see has anyone attempted putting the silencer of the FZ16 on th pulsar?

Can anyone suggest something for the same?

dude there must be some torture going on with tat end cap .. what have u done with it...

[voodoo_god13]

Take a look at this thread. The most reliable source on xbhp.

http://www.xbhp.com/talkies/pit-stop-general-biking-discussion/11542-4-stroke-performance-tuned-free-flow-exhaust.html

[jas_mirage]

dude there must be some torture going on with tat end cap .. what have u done with it...

I swear I didnt do anything to it.. It must have developed its suicidal tendencies by living with me...

[jits2040]

Which exhaust is good for Karizma R

Hi 2 all experts,

I am new member in this community.

I hv Karizma R and i want good performance/free flow exhaust,i have two options and i need your suggestions
1.) KRP Exhaust
2.)Automech Exhaust

Please suggest me which exhaust is good for performance
I already hv K&N airfilter,NGK plug nd cord

Thanxx in advance

[rachitkdogra]

Hi 2 all experts,

I am new member in this community.

I hv Karizma R and i want good performance/free flow exhaust,i have two options and i need your suggestions
1.) KRP Exhaust
2.)Automech Exhaust

Please suggest me which exhaust is good for performance
I already hv K&N airfilter,NGK plug nd cord

Thanxx in advance

Hi There,

I have a 2006 Model Zma and I am using the KRP exhaust for almost more than a year now. I am not sure about the Automech Exhause because I have not heard about it and never seen it. As for the KRP exhaust, it is good. No problems till date. Finishing is nice, no rattling till now and it definately gives a slight boost in the performance throughout rev range (My Observation). It sounds very nice too.