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True dual exhaust is it possible ??? by pontiacfierokid1985
Started on: 01-11-2011 11:09 PM
Replies: 193 (5713 views)
Last post by: Hairold on 07-19-2013 01:00 PM
dobey
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Report this Post06-26-2013 03:49 PM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Arns85GT:
I have an O2 sensor on mine. And I use it. No reason at all not to use one. And, like the man said, the sensor can read one side only and get along just fine.


That's great. But it doesn't really do anything for the engine itself, unless you're reading the data. I never said it "couldn't get along fine." I said "it is a point of potential problems" and "won't necessarily run 100% optimal."

There's a big difference. I wish you people would learn to read, and stop looking at every opposing view to your own biases, as simply negative detraction. It's not.
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Report this Post06-26-2013 04:34 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
A little touchy?

The O2 sensor can only read one thing at one time. Ergo you would need 6 for a 6 cylinder car if you wanted individual cylinder readings. The O2 can take one reading for the electronics system and it does not take 2 of them on a Fiero. So it could be run on just one bank of cylinders.

I use the O2 to measure the gas mixture to ensure I have an optimum burn. In my case it is just a gas mixture sensor, but it is the same sensor. This is the reason the O2 sensor on a Fiero is below the Y. On my engine it is right at the dump flange

Arn

[This message has been edited by Arns85GT (edited 06-26-2013).]

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Report this Post06-26-2013 04:37 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post

Arns85GT

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quote
Originally posted by DimeMachine:


If you have stood at the starting line at a top fuel event you would totally get it (the downforce and forward thrust part). Should be on everyones bucketlist.



Been there, done that

Arn
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Report this Post06-26-2013 08:40 PM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Arns85GT:
Now here are the headers Will has posted. Nicely fabricated and look way better than my 4.9 exhaust.

However, do they offer improved performance? In short no.


I never said they were headers.
I built the rear manifold because I couldn't modify any of the GM offerings to work. If I went with headers, I'd have had to build both, which as you know is much more work. If I'd built headers for just the rear, the banks would obviously be severely imbalanced.
You're drawing a pretty tenuous comparison between my exhaust and the one on your 4.9. Yours is on an engine that makes 200ish HP and mine is on an engine that makes about 350.

 
quote
Originally posted by Arns85GT:
This system has scavenging designed right in. The Magnaflow muffler is actually a perforated straight pipe, and the collector function is satisfied.


No, the front bank and rear bank collectors are different lengths. Collector size and length are critical to the shape of the power curve. This will yield different scavenging effectiveness between the front and rear banks. Unless he's running an ECM with separate fuel trims for each bank, the two banks will NEVER both be running the same AFR. The engine will always be partially out of tune.

[This message has been edited by Will (edited 06-26-2013).]

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Report this Post06-26-2013 09:51 PM Click Here to See the Profile for AsterixClick Here to visit Asterix's HomePageSend a Private Message to AsterixEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
No, the front bank and rear bank collectors are different lengths


On what basis do you state "... the front bank and rear bank collectors are different lengths"? Please be specific.
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Report this Post06-26-2013 09:56 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
You obviously haven't followed Vic Edelbrock's work. In his Torker II design, the left side runners are distinctly narrower than the right side runners to allow one side of the engine more torque in the lower rpm range and the other side more in the upper range.

This same technique is employed in other applications as well. The Asterix engine will not be in a state of distuning.

Yes I agree that I would (and did) make both sides equal to each other, but, for performance, I don't think it will detract.

As for your creation, as I mentioned, it looks great. I expect that when you fabricated it you expected better results than stock manifolds, otherwise why build it? Just my take.

Arn

[This message has been edited by Arns85GT (edited 06-27-2013).]

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Report this Post06-26-2013 09:57 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
Here is an exhaust question for some knowing person. If you want the engine to "see" an exhaust run of 30 inches but you need to move the exhaust a total of 60 inches, how large would the additional 30 inches of pipe have to be for the engine to "think" the run was only 30 inches? I am thinking this would be useful in making equal length exhausts in an install that requires unequal lengths to get to a proper exit point. Larry
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Report this Post06-27-2013 10:07 AM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
Larry this is a new one for me. I know that if the exhaust run makes 72" the negative pulses feed back on themselves and you lose scavenging. I know that most makers are engineering in a break which is part of the X or H in duals or the resonator function. I also know that the formula's I've read do not refer to the phenomenon you are talking about. Can you elaborate?

Anr
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Report this Post06-27-2013 11:00 AM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
At some point an increase in the exhaust pipe diameter must look like the smaller pipe is dumping into open air. An extreme case woud be for a 1 inch exhaust pipe 30 inches long dupming into a 55 gallon drum with an open end that was 30 inches long for a total of 60 inches that the engine thinks is like 30 inches. There must be some point that an increase in exhaust pipe diameter will cause the engine to think that is all the pipe there is. Make sense? Larry
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Report this Post06-27-2013 11:56 AM Click Here to See the Profile for lateFormulaSend a Private Message to lateFormulaEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by trotterlg:

At some point an increase in the exhaust pipe diameter must look like the smaller pipe is dumping into open air. An extreme case woud be for a 1 inch exhaust pipe 30 inches long dupming into a 55 gallon drum with an open end that was 30 inches long for a total of 60 inches that the engine thinks is like 30 inches. There must be some point that an increase in exhaust pipe diameter will cause the engine to think that is all the pipe there is. Make sense? Larry


Ask any ricer. They all know the answer to your question.
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Report this Post06-27-2013 01:32 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
Didn't think I was allowed to talk to Ricers!
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Report this Post06-27-2013 01:56 PM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
Larry, the engine doesn't specifically care, or "know" as you put it, how long the exhaust is. What matters is having pipe of a diameter which doesn't cause the exhaust flow to slow down (or expand) too much, but which is large enough to allow the exhaust to flow freely throughout the RPM range of the engine.

What is it exactly you're trying to accomplish?
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Report this Post06-27-2013 02:26 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
Seems that it is desireable for any duel exhaust to have equal length tubes. With a transverse engine this is not always easy to do, so I was wondering if there was a way to make the engine think it had equal length tubes not really have them. Larry
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Report this Post06-27-2013 03:11 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
The feedback the engine receives from the exhaust is in the nature of a negative pressure pulse. This is hopefully timed to when the exhaust valve is open, to suck the gases as they are forced out by the cylinder. The exact length of the pipe and its diameter change the frequency of these pulses. So essentially, when the pulse reaches an open area like a resonator or collector, the negative pressure pulse disperses. If it doesn' t reach this larger chamber, it just continues on. Eventually it slows down. This causes a ripple back. This is bad. So, the quick answer is you want the pipe to be a length to allow the pulse to last through the piston cycle, but no longer. This is a tough thing to balance, however, if you look at all the manufacturers of headers you will see that on average, their full headers run from about 30" to 36" depending on the application.

If you do the math for your engine, you will come out to a figure somewhere in that range.

The "shorty" headers or medium length headers are used to (a) save money and (b) to accomodate tight quarters in the engine bays. Long tube headers mostly don't fit in engine bays very easily. This is the reason you get "hugger" headers or short ones like the Fiero Store sells.

Hope this helps explain.

Arn

[This message has been edited by Arns85GT (edited 06-27-2013).]

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Report this Post06-27-2013 03:24 PM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by trotterlg:

Seems that it is desireable for any duel exhaust to have equal length tubes. With a transverse engine this is not always easy to do, so I was wondering if there was a way to make the engine think it had equal length tubes not really have them. Larry


With short, or long tube headers? With shorties, I'd have the rear (trunk side) header dump towards the trans, with a U bend into the cat/muffler setup, with a U on the other side, to run back and dump out the driver side. For the front, I'd dump the header towards the trans, and U bend around into the cat/muffler setup for that side, then turn under the frame rail as normal, and go out the passenger side, perhaps with a slight upward U in the pipe toward the end if necessary, to balance out the lengths for each side. It'll be a little easier to do with a manual trans, as you won't have the big snout of the automatics getting in the way. I'd also avoid using huge mufflers, and try to keep them small as well, to conserve space as well. Or just use cats as close to the header exits as possible, and hang a tube style muffler or resonator/silencer right before the tips, to quiet it down a bit.

With that, you should be able to get both sides close enough to equal length for the full system.
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Report this Post06-27-2013 06:36 PM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Asterix:

On what basis do you state "... the front bank and rear bank collectors are different lengths"? Please be specific.


The photos that show 1x 90 degree bend between merge and muffler for one bank and 2x of the same size bend on the other bank.
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Report this Post06-27-2013 07:06 PM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Arns85GT:

You obviously haven't followed Vic Edelbrock's work. In his Torker II design, the left side runners are distinctly narrower than the right side runners to allow one side of the engine more torque in the lower rpm range and the other side more in the upper range.

This same technique is employed in other applications as well. The Asterix engine will not be in a state of distuning.


I'm aware of such silliness with carbed manifolds. That's obviously hack work, as all serious race engines go to exceptional lengths to make sure that all cylinders are running equally well (THE SAME).
The E-I-I-E-E-I-I-E valve arrangement in a Chevy head is an attempt to get the length of all 8 runners in a 4 barrel carbed manifold as close to equal as possible. Obviously, it was recognized as extremely important to the designers of the day and that was 50 years ago.
Look up Barry Grant's inline 4 barrel carb ( http://www.popularhotroddin...ne_carb/viewall.html )
Note that he went to obsessive lengths to assure that mixture quality and quantity were exactly the same for every cylinder... The benefit: previously unheard-of degree of idle quality and mixture distribution and consistent AFR's across all cylinders. If you can't guarantee the same mixture to all cylinders, then you CAN guarantee that some cylinders are NOT running at their best.

So how exactly will the uneven air distribution in Asterix's setup be compensated with appropriate fuel delivery?

 
quote
Originally posted by trotterlg:

At some point an increase in the exhaust pipe diameter must look like the smaller pipe is dumping into open air. An extreme case woud be for a 1 inch exhaust pipe 30 inches long dupming into a 55 gallon drum with an open end that was 30 inches long for a total of 60 inches that the engine thinks is like 30 inches. There must be some point that an increase in exhaust pipe diameter will cause the engine to think that is all the pipe there is. Make sense? Larry


This is related to the impedance of the tube to the propagation of the initial pressure pulse resulting from the blow-down phase of the exhaust.

 
quote
Originally posted by dobey:

Larry, the engine doesn't specifically care, or "know" as you put it, how long the exhaust is. What matters is having pipe of a diameter which doesn't cause the exhaust flow to slow down (or expand) too much, but which is large enough to allow the exhaust to flow freely throughout the RPM range of the engine.

What is it exactly you're trying to accomplish?


The diameter functions as you've said, but the length is related to resonant tuning.

 
quote
Originally posted by Arns85GT:

The feedback the engine receives from the exhaust is in the nature of a negative pressure pulse. This is hopefully timed to when the exhaust valve is open, to suck the gases as they are forced out by the cylinder. The exact length of the pipe and its diameter change the frequency of these pulses. So essentially, when the pulse reaches an open area like a resonator or collector, the negative pressure pulse disperses. If it doesn' t reach this larger chamber, it just continues on. Eventually it slows down. This causes a ripple back. This is bad. So, the quick answer is you want the pipe to be a length to allow the pulse to last through the piston cycle, but no longer. This is a tough thing to balance, however, if you look at all the manufacturers of headers you will see that on average, their full headers run from about 30" to 36" depending on the application.

If you do the math for your engine, you will come out to a figure somewhere in that range.


As the exhaust valve cracks open on residual cylinder pressure, a high pressure pulse propagates from the valve down the primary runner at the speed of sound. At the end of the primary pipe, the abrupt change of impedance (in the wave mechanics sense) causes the pulse to reflect. Some of the energy goes out the end of the primary pipe as noise, some of it is reflected back up the primary pipe as a LOW pressure pulse. At the tuning RPM, the low pressure pulse arrives as the exhaust valve is closing, it assists in scavenging the last of the exhaust out of the cylinder. It ALSO continues to propagate up the intake primary, as the intake valve is just opening and provides energy to kickstart the intake pulse tuning phenomenon.

If you do the math on the speed of sound in ~1000 degree exhaust gas, you'll find that for something "normal" like the L98 tuned port 350 (considering the stock exhaust valve duration), the "first reflection" sequence I described above requires a pipe length of ~120 inches to operate at the engine's 3500 RPM torque peak.
Obviously that's too long to be practical. However, 1/4 of that distance is practical. So with a tuned length of ~30 inches, the high pressure pulse will bounce back and forth between the valve and the collector 4 times... hence the "4th reflection" that I asked you about previously. The pulse will reverse polarity each time, as both ends are open pipe reflections. When going downstream it's always a high pressure pulse; when going up stream it's always low pressure.

That's how tuned lengths work.

Collectors function similarly, but using the output of all primary tubes and with lower velocities.

The pipe diameter derives from what Dobey said... Getting the right velocity coming out of the exhaust port. That's why mass, density and residual pressures are important. Go read on the advanced tech form at www.speedtalk.com

[This message has been edited by Will (edited 06-27-2013).]

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Arns85GT
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Report this Post06-28-2013 09:53 AM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
Will, you are confusing issues.

The pneumatic pressure pulse is a different issue to sonic flow.

Sound waves do not equal gas pounds per square inch in this application. The pressure pulse traveling down the pipe creates a negative wake as it moves down and that is scavenging. The sound wave will occur, I agree, but it is outweighed by the pneumatic pressure.

Arn
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Report this Post06-29-2013 09:52 PM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Arns85GT:

Will, you are confusing issues.

The pneumatic pressure pulse is a different issue to sonic flow.

Sound waves do not equal gas pounds per square inch in this application. The pressure pulse traveling down the pipe creates a negative wake as it moves down and that is scavenging. The sound wave will occur, I agree, but it is outweighed by the pneumatic pressure.

Arn




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Report this Post06-30-2013 09:33 AM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
He was referring to the sound wave created by the gas travelling at the speed of sound. It is absolutely true a sonic wave is created, however, it only travels one way. Without something to catch the wave and cause it to reflect back, it just continues on.

The pneumatic pulse however, pushes air forward and creates a negative air pressure pocket behind it.

Two different things.

Arn
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Report this Post07-01-2013 09:00 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Arns85GT:

Will, you are confusing issues.

The pneumatic pressure pulse is a different issue to sonic flow.

Sound waves do not equal gas pounds per square inch in this application. The pressure pulse traveling down the pipe creates a negative wake as it moves down and that is scavenging. The sound wave will occur, I agree, but it is outweighed by the pneumatic pressure.

Arn


There are two different phenomena that operate simultaneously. BOTH have been proven and are commonly accepted.

The flow velocity through the port will not be sonic, but the pressure pulse created by opening the valve will be.

The primary diameter bears far more heavily on the momentum effect, while primary length bears on the pulse effect.
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Report this Post07-01-2013 09:03 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post

Will

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quote
Originally posted by Arns85GT:

Without something to catch the wave and cause it to reflect back, it just continues on.



How do pipe organs work? (or any other open pipe musical instrument)

Google "Open Pipe Reflection"
There's a whole world of wave mechanics waiting
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Report this Post07-01-2013 01:17 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
Luckily I am a long time musician.

A sound wave does not rely on moving air from point A to point B. If it did, a loud music note would come across like a hurricane. Notice that at a rock concert you can "feel" the bass notes but the force is not blowing you off your feet.

You can find a full explanation here

Sound is measured by a unit of Hertz. 1 Hertz = 1 vibration per second. The vibrations occur as a wave motion, not a forward motion. It is a back and forth motion.

A pneumatic pulse is generated by compressed gas being released at intervals. This does move compressed or pressurized gas forward and is used to power tools. It is also the basis of the steam engine.

A pneumatic pulse occurs when the exhaust valve opens, and pressurized gas is forced by the piston, out the hole and down the pipe. As it moves down the pipe, there is a vacuum created in its wake. This pneumatic phenomenon is the basis for "scavenging". That is to say to apply a width of pipe and length of pipe that allows the pulse of gas to pull the vacuum along at the optimum distance and at the optimum speed.

If you reference all the leading header makers, you will see a commonality in the size and length of primary pipes they use.

Most common is 1.5" x 22+". This varies as to whether you are building full length, mid length or sort length headers. Anything under 22" is not effective. The preferred length, of performance has continued to be, for many many years in the 30" to 36" length.

When you designed your exhaust, you can see that you did not design them with header theory in mind.



Notice the very short runners with a combined plenum exiting to a pipe. This is essentially the type of thing that GM did for it's engines. It works, but it is not a scavenging style system and while it functions well enough, it is not a high performance design.

Hope this explains

Arn
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Report this Post07-01-2013 01:51 PM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Arns85GT:
When you designed your exhaust, you can see that you did not design them with header theory in mind.


Stop being an idiot and trying to imply that Will designed the manifolds. It's pretty obvious that front manifold is completely stock, and the rear is a basic log style manifold made to fit and perform as equally as well as the front stock manifold, as a stock manifold wouldn't fit due to interference, as Will already clearly stated. Obviously they weren't designed with header theory in mind. And I'm sure if Will wanted to design a set of optimally performing headers within the constraints of the Fiero engine bay so that it would actually fit, then he could do it. He didn't post that picture as an example of optimal header design. He posted it as an example of "true dual" in a Fiero, which he put together, even if he didn't build custom headers for it.
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Report this Post07-01-2013 03:08 PM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Arns85GT:

Luckily I am a long time musician.



*SIGH*

Then you should understand why this is NOT correct:

 
quote
Originally posted by Arns85GT:

it only travels one way. Without something to catch the wave and cause it to reflect back, it just continues on.


Changes of impedance for ANY wave create both reflections and refractions. This is the principle whereby open pipe winded musical instruments operate.

The excitation of a woodwind instrument is constant, while the resonant properties of the system concentrate the broad spectrum energy from the musician's lungs into single tones. The excitation of the header pipe is not constant; therefore a header pipe is a time domain system while a musical instrument is best understood in the frequency domain.
If all the energy of the wave exited the open end of the pipe, the instrument would just be a megaphone reproducing the farting noise the musician makes with the reed.
The reflection back INTO the instrument from the open end of the pipe is what provides for the constructive/destructive interference which kills off the frequencies in the excitation that are out of the resonant band for that tone.

Read this: http://en.wikipedia.org/wik...domain_reflectometer

I don't have time to teach you all this... Just recognize that there's a heck of a lot out there that you don't seem to get... Follow my research recommendations and you'll get started as well as find some additional topics to read up on.

Or don't... my car won't be any slower for your refusal to research.

You're not reading my posts anyway, or you would have read more than once why I built my exhaust the way I did.

[This message has been edited by Will (edited 07-01-2013).]

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Report this Post07-01-2013 05:10 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
Sigh, yes Will I understand you fabricated one side. The whole setup is not anything better than OE exhaust. Yes. I agree.

So with your theory, a trumpet player who makes the pulsating air with his lips, has that sound modified by the gradually increasing trumpet pipe which "feeds back"? Not hardly.

Syn waves are one way until they reflect off a surface.

You didn't read my link.

 
quote
the resonant properties of the system concentrate the broad spectrum energy from the musician's lungs into single tones.


You are insinuating that the tonal qualities of the lungs of the trumpet player, (or clarinetist) affect the tone of the instrument?
There are a variety of different people who can play a similar instrument and achieve similar tone. A 95 lb woman can use a clarinet the same as a 200lb man. Albeit her lungs have less capacity so she likely won't achieve the same maxiumum volume over a span of time.

 
quote
The reflection back INTO the instrument from the open end of the pipe is what provides for the constructive/destructive interference which kills off the frequencies in the excitation that are out of the resonant band for that tone.


Wrong. The choice of media to create the tube moderates the frequencies. Same thing in some car mufflers like the glass pack or the Magnaflow.

You can talk theory, but the reality of application is pretty much established over many years with both musical instruments and with car engines.

The issue is different with a violin. The sound waves generated by the bridge are connected with a post to the back and that makes the back and front vibrate in unison. Whereas the wind instrument has the syn wave moderated by the type of material the tunnel or horn is made of. This varies between silver, brass, rosewood, mahogany, etc. It has nothing to do with sound waves traveling back up stream. The gradually expanding tube of the trumpet, for instance, makes it loud and piercing.

The pneumatic pulse though, is entirely different. It telegraphs a negative pulse behind it because it is generating a negative field of pressure as it pulls the gas through the tube. If the tube gets too long, the gas slows down causing the negative pulses to overlap destroying the scavenging efficiency. There is a pneumatic pulse in a trumpet too, but it is minor compared to the amplification of the syn wave.

Please don't try to school me on music. You'll have the wrong guy.

Arn

[This message has been edited by Arns85GT (edited 07-01-2013).]

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Report this Post07-01-2013 06:46 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
This is the 'syn' or sine wave



Notice how it moves forward back and forth. As you increase the amplitude, you increase the volume. As you increase the wave length, you lower the note. This is how you get an exhaust to sound deep. You set your pipe size to allow the longer length waves to travel while giving the shorter waves with smaller amplitude a not so friendly environment so the 'high notes' don't travel as well. This is over simplifying, but it shows why a 2.5" pipe gives a deeper bark than the 2" pipe.

Arn
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Report this Post07-01-2013 10:03 PM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Arns85GT:
Please don't try to school me on music. You'll have the wrong guy.


You see, the problem with this statement and attitude, is that musical or liberal arts colleges are not exactly known for STEM. Just because you know how to play a guitar, and make noise that you think sounds good to your own ears, does not mean you are a physicist in the realm of fluid dynamics, or have any education relative to it, at all. Knowing how to play an instrument does not mean you necessarily know or understand how that instrument produces its sounds.

Music is totally unrelated. Though, you keep trying to prove you are somehow right. Will was simply making an example comparison, between wind based instruments, and the exhaust system, because the way the sound and the tone of that sound are managed, is done in the same way.

Stop trying to protect your ego, and go back and try to comprehend what he actually said.
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Report this Post07-01-2013 10:48 PM Click Here to See the Profile for JamesCurtisClick Here to Email JamesCurtisSend a Private Message to JamesCurtisEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yes, it is very clear that Will has a deep understanding of the theory of fluid dynamics as well as physics and Arns is pulling at straws from some books he's read and his past musical experience. I just read a chapter about exhaust and intake tuning from "Introduction to Internal Combusion Engines" by Richard Stone and it frustrates me that he says you need to design your intake and exhaust system to take advantage of these "pulses" but it does not go into detail about how to mathematically achieve what you are looking for. One thing I don't understand is how this "pulse" moving backwards towards the exhaust valve is actually helping scavenge. It would seem to me that any energy moving backwards towards the exhaust valve would be a bad thing unless it was carrying low pressure with it.
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Report this Post07-02-2013 07:52 AM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
I am sure you can agree that no one in this discussion has written the book on the subject and we all rely on what we read.

There really is no pulse that moves back up the pipe. What we are talking about is a negative air pressure pocket that is created by the high pressure pulse moving down the pipe. It follows the high pressure pulse, and the negative pressure pulls the next high pressure pulse along if you time it correctly.

If you work with musicians, and/or are, or have been, involved in the musical instrument industry, you gain an understanding of how they work. This is also found in books. I agree the example given initially was not actually relevent to exhaust design.

It is very possible to overthink what is a known application.

Arn
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Report this Post07-02-2013 08:14 AM Click Here to See the Profile for AustralianClick Here to visit Australian's HomePageClick Here to Email AustralianSend a Private Message to AustralianEdit/Delete MessageReply w/QuoteDirect Link to This Post
Does any engine benefit from having separate exhausts?
The reason y pipes exist is to balance out pressure as the most important part of the engine is the exhaust. It is possible to make a sweet sounding motor with true dual but it is sure to shorten life of motor as once one side blows more pressure it will lack true performance. In realiity there would be less performance as the engine of facing the wrong direction to benefit with having separate exhausts.
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Report this Post07-02-2013 09:57 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Arns85GT:

So with your theory, a trumpet player who makes the pulsating air with his lips, has that sound modified by the gradually increasing trumpet pipe which "feeds back"?


Correct. The trumpet player makes a buzz with his lips, the sax player makes a buzz with the reed. The buzz has a broad variety of frequencies in it. The tuned length of the instrument creates standing waves that collect that broad range of frequencies into a single tone. Well... it's not really a single tone as the output of any musical instrument is spectrally complex, BUT the instrument transforms the frequency content of the buzz into that of the note the musician is playing. By opening and closing valves to change the tuned length, the musician changes the note, even though he's still making the same buzz at the input.

That has very little to do with tuned exhaust as it is a FREQUENCY DOMAIN system. The exhaust is a TIME DOMAIN system.
http://en.wikipedia.org/wiki/Frequency_domain
http://en.wikipedia.org/wiki/Fourier_transform

 
quote
Originally posted by Arns85GT:
Syn waves are one way until they reflect off a surface.



Then how does a thermocline in the ocean reflect sonar waves?
How does a mirage form?
Every interface between different propagation media--for ALL WAVES, electromagnetic or sonic--or even the same media at different temperatures with different indices of refraction, creates both a reflection and a refraction. That's why you can create an echo from the surface of a pool, but also hear the same sound underwater.

 
quote
Originally posted by Arns85GT:

You didn't read my link.


Don't need to. I took sophomore physics in 1997. It doesn't change. No, I don't need a refresher.

 
quote
Originally posted by Arns85GT:

You are insinuating that the tonal qualities of the lungs of the trumpet player, (or clarinetist) affect the tone of the instrument?


Nope. That's not what I said.

 
quote
Originally posted by Arns85GT:

Wrong. The choice of media to create the tube moderates the frequencies. Same thing in some car mufflers like the glass pack or the Magnaflow.


The tuned length creates the fundamental. The material adds overtones that make the musical instrument a musical instrument instead of a tone generator. See my comment above about spectral complexity.

By your theory, the buzz that the player creates should come right out the end of the instrument. In the theory you've advanced, there's no mechanism that creates different notes. If sound and wave mechanics worked the way you think they do, there wouldn't be any difference between playing a sax and spitting a razberry into an exhaust pipe. Your theory doesn't explain how opening and closing valves creates different notes.

 
quote
Originally posted by Arns85GT:

The issue is different with a violin.


A violin is a helmholtz resonator.

 
quote
Originally posted by Arns85GT:

This is the 'syn' or sine wave





That is a sine function. It's one of the ordinary trigonometric functions; the others being cosine, tangent, cotangent, secant and cosecant. Don't call it a "syn"; that makes you look mathematically illiterate.

I'm intimately familiar with the properties of sine functions. They are one of the main classes of solutions to differential equations.

OBTW, I have degrees in physics, mathematics and systems engineering. I wasn't going to make that appeal to authority, but since you opened the door by claiming musical expertise, there you go.

Argument from authority is a logical fallacy, as it does not establish the correctness of the argument. https://en.wikipedia.org/wiki/Argument_from_authority#Fallacious_appeal_to_authority

[This message has been edited by Will (edited 07-02-2013).]

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Report this Post07-02-2013 10:02 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post

Will

13333 posts
Member since Jun 2000
 
quote
Originally posted by JamesCurtis:
One thing I don't understand is how this "pulse" moving backwards towards the exhaust valve is actually helping scavenge. It would seem to me that any energy moving backwards towards the exhaust valve would be a bad thing unless it was carrying low pressure with it.


The motion of energy and the motion of matter are different things.
Sound waves travel and convey energy at a speed relative to the air.
The speed of sound at standard temperature and pressure (sea level pressure, 70 degrees temperature) is ~1100 feet per second.
If you shout into a 30 mph wind (~48 feet per second), the sound you create is moving 1052 fps relative to the ground, but still moving 1100 fps relative to the air it's moving through. People upwind can still hear you because the energy in your sound waves reaches them, even though the air through which that energy is travelling is moving in the opposite direction.
If you shouted downwind, then your shout would be travelling at 1148 fps.
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Report this Post07-02-2013 10:46 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Arns85GT:

we are talking about is a negative air pressure pocket that is created by the high pressure pulse moving down the pipe.



This does happen. It happens at the same time as the pulse phenomenon I'm talking about.

The exhaust stroke can be readily divided into two phases: blow down and pump down. During blow down, the cylinder pressure significantly exceeds atmospheric and the potential energy from the gas pressure is converted to kinetic energy as it pushes the gas out of the cylinder and down the primary tube, as well as acoustic energy.
During pump down, the cylinder pressure has dropped to approximately atmospheric and the exhaust gas moves out of the cylinder as the piston pushes it.

Soo...
When the exhaust valve cracks, there's residual pressure in the cylinder to the tune of a couple hundred psi. The sudden release of this pressure creates a high amplitude sound wave (It's not a shock wave as nothing is exceeding the speed of sound). This high amplitude sound wave kickstarts the time domain process I outlined previously. This pulse travels at the speed of sound, which is ~1800 fps in exhaust gas at ~1000F.

At the same time, the pressure blows down the cylinder to create a high velocity "plug" of exhaust gas that imparts momentum to the exhaust stream during the blow down phase. The numbers I've read for the ideal port velocity are in the range of 700 fps. This number is very difficult to find... The primary factor relating the cylinder content in terms of mass, temperature and pressure to port velocity is the DIAMETER of the primary pipe. The length of the pipe doesn't affect this phenomenon very much. As long as the pipe isn't so long that wall friction reduces the velocity (or there are multiple plugs in the pipe at the same time) or so short that the plug exits the pipe well before the exhaust valve closes, this phenomenon is quite tolerant of a wide range of lengths in primary pipe. "Long" and "short" as used here mean relative to the exhaust valve open time, which is a function of exhaust valve duration in degrees and desired tuning RPM.

The momentum created during the blowdown phase serves essentially to act like a piston in a vacuum pump to create a draw on the exhaust port at some point in time during the pump-down phase. At the tuning RPM, this draw occurs just as the exhaust valve is closing and helps to draw the last bit of exhaust out of the chamber.

However, this draw isn't a pulse. It doesn't have a sharp rise time, so it doesn't propagate through the valve overlap period to provide energy to kickstart a time domain process in the intake tract. The pulse phenomenon I outlined DOES propagate through the valve overlap and kickstart the intake process.

[This message has been edited by Will (edited 07-02-2013).]

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Report this Post07-02-2013 10:59 AM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
Nice explanation Will. BTW I was not talking about pitch which you rightfully point out is changed by the opening of valves on the wind instrument.

And, you've explained in more detail, how the pulse travels down the pipe and how the vacuum is generated behind it.

I think we can agree that the length of the pipe speaks to the timing of the dispersion of the pulse and that allows a person to 'tune' the pipe length.

For the sequentially firing V6, the industry wide conclusion appears to be as I have stated. If you look at the products produced by the makers, that is to say full headers made by Hedman, etc. Their products have great similarity.

BTW a 4 cylinder bank of cylinders is a whole different kettle of fish and good for a separate discussion for the swappers.


Arn
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Report this Post07-02-2013 12:17 PM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Arns85GT:

I think we can agree that the length of the pipe speaks to the timing of the dispersion of the pulse and that allows a person to 'tune' the pipe length.


No we can't. The length of the pipe is tuned most sharply by the time-domain phenomenon I've been talking about.

 
quote
Originally posted by Arns85GT:
For the sequentially firing V6, the industry wide conclusion appears to be as I have stated.


No. See previous discussion about BMW's.

 
quote
Originally posted by Arns85GT:
BTW a 4 cylinder bank of cylinders is a whole different kettle of fish and good for a separate discussion for the swappers.

Arn


No, an even-fire 4 cylinder is exactly the same.
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Report this Post07-02-2013 12:30 PM Click Here to See the Profile for JamesCurtisClick Here to Email JamesCurtisSend a Private Message to JamesCurtisEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Will:


The motion of energy and the motion of matter are different things.
Sound waves travel and convey energy at a speed relative to the air.
The speed of sound at standard temperature and pressure (sea level pressure, 70 degrees temperature) is ~1100 feet per second.
If you shout into a 30 mph wind (~48 feet per second), the sound you create is moving 1052 fps relative to the ground, but still moving 1100 fps relative to the air it's moving through. People upwind can still hear you because the energy in your sound waves reaches them, even though the air through which that energy is travelling is moving in the opposite direction.
If you shouted downwind, then your shout would be travelling at 1148 fps.


Will,

Thank you for further explaining this and you may have answered my question I am just lack the intellect to realize it. I still don't see how this energy moving backwards down the pipe and reaching the exhaust port with the exhaust valve open increases scavenging. Can you go into further detail on what's happening as the pulse reaches the open exhaust valve and the physics behind the forces increasing the scavenging? I am currently moving towards a degree in electrical engineering and I am greatly looking forward to the thermodynamics class that I will take along the way .

Thank you!

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Report this Post07-02-2013 02:04 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Will:


No, an even-fire 4 cylinder is exactly the same.


Sorry, I was not referring to even fire 4 bangers. I was referring to the GM V8's with the odd firing order. I should have been more specific. You get the 4 into 1 vs. the 4 into 2 into 1 and that changes the power curve. A whole different consideration than the sequential engines.

Arn
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Report this Post07-02-2013 05:43 PM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Arns85GT:

The whole setup is not anything better than OE exhaust.


There's no such thing as an OE exhaust in a Northstar Fiero.

The stock manifolds have 2" outlets. I cut the outlet off the front manifold, cut the manifold back until it had the same circumference as a 2.5" pipe, "massaged" it to shape and welded on a 2.5" flex section and V-band flange.

 
quote
Originally posted by Arns85GT:

Sorry, I was not referring to even fire 4 bangers. I was referring to the GM V8's with the odd firing order. I should have been more specific. You get the 4 into 1 vs. the 4 into 2 into 1 and that changes the power curve. A whole different consideration than the sequential engines.

Arn


I'm curious about how collecting the two evenly spaced cylinders into one sized collector, then collecting the two sequential cylinders into a larger collector, then merging those two would affect the powerband... simply a Tri-Y with different secondary sizes.

But mostly I'd rather build 180 degree headers.
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Report this Post07-02-2013 05:50 PM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by JamesCurtis:

Will,

Thank you for further explaining this and you may have answered my question I am just lack the intellect to realize it. I still don't see how this energy moving backwards down the pipe and reaching the exhaust port with the exhaust valve open increases scavenging. Can you go into further detail on what's happening as the pulse reaches the open exhaust valve and the physics behind the forces increasing the scavenging? I am currently moving towards a degree in electrical engineering and I am greatly looking forward to the thermodynamics class that I will take along the way .

Thank you!


You're welcome.
A significant amount of the body of knowledge regarding transmission lines is applicable to header design. That's why I kept referring to the impedance of the pipe to the propagation of the sound wave.
If you're in electrical engineering, take a course in transmission lines and microwave/RF techniques. When I was in college for Physics, I did this based on the recommendation of an old electrical engineer I worked with during my summer job at the Naval Research Lab. The course was very helpful in giving a practical background to the generalized discussion of fields, as well as a solid understanding of wave mechanics.

Basically, my entire argument could be summarized by this graphic:



From the time domain reflectometer article: http://en.wikipedia.org/wik...domain_reflectometer
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