Exhaust Wraps versus Performance

[RideFree]

I started asking for information on this in the Twin Cam thread as it relates to cam overlap and scavenging but thought I would bring it out on its own in the General Forum. What I am thinking and looking for evidence of, such as dyno results, is proof that exhaust wraps do not increase performance but rather decreases it by 1 to 2%. Or evidence to the contrary.

Empirical evidence suggests wraps are nothing more than leg coolers. I have not seen a wholesale use in racing circles and if it increased performance at all they would be the ones to all be using it. It's very cheap and easy to install and looks cool so why not if it increases performance, as we all are always looking to get a little more out of our bikes within our own monetary capabilities. However, I do not see that.

More to physical evidence is the volumetric decrease that occurs as a gas cools. I have heard the analogy for wraps to fluids for keeping the exhaust gases hot so they keep flowing better. However, I do not think comparing how fluids flow with temperature changes applies to gases. For gases I think the volumetric decrease as a gas cools overshadows any resistance to flow. Look at tuned pipes and their step increases in diameter to get the exhaust gasses to expand thus creating lower pressure areas that help continue to draw the exhaust away from the cylinder. Add cooling to that i.e., no wraps, and it should lower the pressure and draw even more which could help scavenge even more during overlap.

I have only read one dyno operator say they have seen that wraps decrease performance, any others or to the contrary? Note that was a car dyno.

[Matt C]

Those steps are more for sonic wave action than actual gasflow. When the sound wave hits that expansion, it reflects a negative
pulse back at the ex port, so what you get is a series of negative pulses while the valve is open, and one big pulse when it hits the
end of the pipe (hopefully right before the valve closes during overlap). All this helps scanenge the cylinder and pull in fresh charge.

But wrapping the pipe definately keeps the velocity high. That's not even up for debate, it's scientific fact.

P.S. Forget fluid, that's a whole different thing. (fluid is not compressable)

[Matt C]

If you've ever been to the Harley drags, you'll see lots of wrapped pipes.

[Admiral Akbar]

Those steps are more for sonic wave action than actual gasflow. When the sound wave hits that expansion, it reflects a negative
pulse back at the ex port, so what you get is a series of negative pulses while the valve is open, and one big pulse when it hits the
end of the pipe (hopefully right before the valve closes during overlap). All this helps scanenge the cylinder and pull in fresh charge.

But wrapping the pipe definately keeps the velocity high. That's not even up for debate, it's scientific fact.

P.S. Forget fluid, that's a whole different thing. (fluid is not compressable)

Coupla things..

It's not sonic waves that are tuned in an exhaust system, it's gas flow pulses..   They are different.. Sonic waves really don't have any energy..

How much higher does it keep the velocity?  If it's a scientific fact, it has to be documented somewhere..

I would expect that wrapping the pipe does keep the volume slightly higher.. If it keeps the volume higher all it really does is make the exhaust system seem a little smaller...  If the system is oversized, it may help.. If the exhaust system is undersized, wrapping might hurt..

Max

[Hillside Motorcycle]

.................and in automotive application the wrap helps reduce under-hood temps...........helping to keep the engine's incoming air temps lower.

[Matt C]

Those steps are more for sonic wave action than actual gasflow. When the sound wave hits that expansion, it reflects a negative
pulse back at the ex port, so what you get is a series of negative pulses while the valve is open, and one big pulse when it hits the
end of the pipe (hopefully right before the valve closes during overlap). All this helps scanenge the cylinder and pull in fresh charge.

But wrapping the pipe definately keeps the velocity high. That's not even up for debate, it's scientific fact.

P.S. Forget fluid, that's a whole different thing. (fluid is not compressable)

Coupla things..

It's not sonic waves that are tuned in an exhaust system, it's gas flow pulses..   They are different.. Sonic waves really don't have any energy..

How much higher does it keep the velocity?  If it's a scientific fact, it has to be documented somewhere..

I would expect that wrapping the pipe does keep the volume slightly higher.. If it keeps the volume higher all it really does is make the exhaust system seem a little smaller...  If the system is oversized, it may help.. If the exhaust system is undersized, wrapping might hurt..

Max

Its BOTH! Why do you think header primary tubes are a "tuned" certain length? They're cut to the
length that makes the sound wave arrive back at the port at just the right time. (Usually just before
the ex. valve closes)

There are TWO things at work in an exhaust system. Gas flow and Sonic waves. It's a very complex
interaction but you cannot condiser one without the other if you want to maximize the power produced.

P.S. Sonic waves have a considerable amount of energy.

[Matt C]

Coupla things..

It's not sonic waves that are tuned in an exhaust system, it's gas flow pulses..   They are different.. Sonic waves really don't have any energy..

How much higher does it keep the velocity?  If it's a scientific fact, it has to be documented somewhere..

Its documented in physics books, or look up universal gas law, boyle's law, charles' law. You can transpose
these equasions to solve for temperature pressure or whatever.

I think some people are calling with sonic pulses "gas flow pulses". Sonic pulses definately play a huge role
in pipe tuning. Thats why a header pipe is tuned to a certain length. It's tuned for sound, not some arbitrary
gasflow number.

Lowering the temperature of a moving gas will: 1. make it more dense 2. remove energy 3. slow it down
Look, I'm not here to argue. If you don't want to believe what I'm saying, I really don't care.

Do your own research, I'm not going to debate you on something I know to be true. Go grab some physics
books and look it up

[rbabos]

A wrap will trash the pipe quicker.
Ron

[Admiral Akbar]

Its BOTH! Why do you think header primary tubes are a "tuned" certain length? They're cut to the
length that makes the sound wave arrive back at the port at just the right time. (Usually just before
the ex. valve closes)

There are TWO things at work in an exhaust system. Gas flow and Sonic waves. It's a very complex
interaction but you cannot consider one without the other if you want to maximize the power produced.

P.S. Sonic waves have a considerable amount of energy.

Lets say the sound pressure at the exhaust opening is 140 decibels..  (stick your ear right next to the end of the pipe)

That would make the sound pressure pulse about 200 pascals or 0.029 psi   

When dealing with a range of 14.7 psi.. It's only about 0.2% of ambient..  Doesn't seem like much energy to me.. Anyone ever actually measure the sound energy?

Max

[Admiral Akbar]

A wrap will trash the pipe quicker.
Ron

I would agree.
While some like to use a special ceramic coating on the inside of the pipe and I suspect that it might help a little.. Dragos?   I prefer a special carbonic coating that requires a bit of time to apply..

Max
 

[rbabos]

A wrap will trash the pipe quicker.
Ron

I would agree.
While some like to use a special ceramic coating on the inside of the pipe and I suspect that it might help a little.. Dragos?   I prefer a special carbonic coating that requires a bit of time to apply..

Max

Took me most of the season to do my pipes. Can't tell the difference other than sound maybe
Ron

[Matt C]

Its BOTH! Why do you think header primary tubes are a "tuned" certain length? They're cut to the
length that makes the sound wave arrive back at the port at just the right time. (Usually just before
the ex. valve closes)

There are TWO things at work in an exhaust system. Gas flow and Sonic waves. It's a very complex
interaction but you cannot consider one without the other if you want to maximize the power produced.

P.S. Sonic waves have a considerable amount of energy.

Lets say the sound pressure at the exhaust opening is 140 decibels..  (stick your ear right next to the end of the pipe)

That would make the sound pressure pulse about 200 pascals or 0.029 psi   

When dealing with a range of 14.7 psi.. It's only about 0.2% of ambient..  Doesn't seem like much energy to me.. Anyone ever actually measure the sound energy?

Max

Im quite sure you can find LOTS of published papers on this. Those sound waves are not insignificant. Ever looked at
a two-stroke expansion chamber? Those divergent and convergant cones you see are strictly designed to harness the
sonic energy from the sound wave that occurrs when the EX port opens. The only difference is, the sound wave is reflected
as a positive pulse as opposed to a negative one.

An open megaphone reflects a negative wave, a megaphone with a convergent cone attached reflects a positive signed wave.
That positive signed wave in the two-stroke pushes unburned gasses back into the cylinder just before the piston
closes the port. That pressure wave is quite strong. Don't ask me to calculate it, I've forgotten most of that stuff.

[Matt C]

A wrap will trash the pipe quicker.
Ron

You got that right! Ceramic coatings do the same thing (keep the heat IN the pipe) and
they look much nicer. You can coat the outside and get the same affect.

[joe_lyons]

I thought the steps had something to do with the heat expansion and the velocity of it and the wrap or ceramic coating helps keep the heat in so the velocity stays high.

[14Frisco]

Lowering the temperature of a moving gas will: 1. make it more dense 2. remove energy 3. slow it down

What is the temperature difference of the exhaust gas (the gas, not the pipe) when the pipe is wrapped vs. when it is not wrapped?

[rbabos]

Lowering the temperature of a moving gas will: 1. make it more dense 2. remove energy 3. slow it down

What is the temperature difference of the exhaust gas (the gas, not the pipe) when the pipe is wrapped vs. when it is not wrapped?

Roughly 10%. The way it works is the hotter gas has more pressure in the pipe than a cooler gas so the tranfer to atmosphere out the end is faster.
Ron

[14Frisco]

Lowering the temperature of a moving gas will: 1. make it more dense 2. remove energy 3. slow it down

What is the temperature difference of the exhaust gas (the gas, not the pipe) when the pipe is wrapped vs. when it is not wrapped?

Roughly 10%. The way it works is the hotter gas has more pressure in the pipe than a cooler gas so the tranfer to atmosphere out the end is faster.
Ron

Did you measure the 10% temperature difference on a Harley?

[rbabos]

Lowering the temperature of a moving gas will: 1. make it more dense 2. remove energy 3. slow it down

What is the temperature difference of the exhaust gas (the gas, not the pipe) when the pipe is wrapped vs. when it is not wrapped?

Roughly 10%. The way it works is the hotter gas has more pressure in the pipe than a cooler gas so the tranfer to atmosphere out the end is faster.
Ron

Did you measure the 10% temperature difference on a Harley?

No, just a ballpark hotrod figure. I find the whole exercise pointless but that's just me.
Ron

[Cracked Head]

Its BOTH! Why do you think header primary tubes are a "tuned" certain length? They're cut to the
length that makes the sound wave arrive back at the port at just the right time. (Usually just before
the ex. valve closes)

There are TWO things at work in an exhaust system. Gas flow and Sonic waves. It's a very complex
interaction but you cannot consider one without the other if you want to maximize the power produced.

P.S. Sonic waves have a considerable amount of energy.

Lets say the sound pressure at the exhaust opening is 140 decibels..  (stick your ear right next to the end of the pipe)

That would make the sound pressure pulse about 200 pascals or 0.029 psi   

When dealing with a range of 14.7 psi.. It's only about 0.2% of ambient..  Doesn't seem like much energy to me.. Anyone ever actually measure the sound energy?

Max

The work that Gordon P Blair provided in his book of modeling the 4 stroke engine,will verify what you ask.Most engine simulations are from the result of Blair and others work on the theory and proof what what they labeled as finite amplitude waves.The pressure ratios are far above the loudest acoustic pressure  ratios.Modern pressures transducers pretty much verify the chapter in Blairs SAE book of unsteady gas flow dynamics.This book will give you enough formula and experimentation results to make your own simulation models if you are in love with the math.Go over to speed talk and check out Vannicks program and find out what it was based on.

[Matt C]

Lowering the temperature of a moving gas will: 1. make it more dense 2. remove energy 3. slow it down

What is the temperature difference of the exhaust gas (the gas, not the pipe) when the pipe is wrapped vs. when it is not wrapped?

Hell I don't know. Why don't you get some temperature transducers and measure it? Than get back to us.

[Cracked Head]

Professor Blairs bio
http://www.profblairandassociates.com/GPB_Tribute.html

[Admiral Akbar]

The work that Gordon P Blair provided in his book of modeling the 4 stroke engine,will verify what you ask.Most engine simulations are from the result of Blair and others work on the theory and proof what what they labeled as finite amplitude waves.The pressure ratios are far above the loudest acoustic pressure  ratios.Modern pressures transducers pretty much verify the chapter in Blairs SAE book of unsteady gas flow dynamics.This book will give you enough formula and experimentation results to make your own simulation models if you are in love with the math.Go over to speed talk and check out Vannicks program and find out what it was based on.

Blair mentions acoustic waves and spends about a page on it (Fred says "boo") then promptly moves on to finite analysis after stating that it's power would have little effect.. He mentions a rifle shot of 200 decibels only multiplies the pressure by 1.02 or say 2%

Smith's 1968 book dedicates a chapter on sound but moves on to pressure waves..  I think Smith wasn't sure it had any value except reference to exhaust quietness. He goes on to develop a pressure sensing device and measures the corresponding pressure waves..

Max

[Admiral Akbar]

Im quite sure you can find LOTS of published papers on this. Those sound waves are not insignificant. Ever looked at
a two-stroke expansion chamber? Those divergent and convergant cones you see are strictly designed to harness the
sonic energy from the sound wave that occurrs when the EX port opens. The only difference is, the sound wave is reflected
as a positive pulse as opposed to a negative one.

An open megaphone reflects a negative wave, a megaphone with a convergent cone attached reflects a positive signed wave.
That positive signed wave in the two-stroke pushes unburned gasses back into the cylinder just before the piston
closes the port. That pressure wave is quite strong. Don't ask me to calculate it, I've forgotten most of that stuff.

Absolutely.. Have Jennings book sitting on the shelf right in front of me.. It's not sound but pressure waves that are reflected..

Blair and Atherton say no.. BTW Athertons book Desktop dynos is a pretty easy read though I think he screws up on the discussion of the Kadenacy theory. 

Max

[Matt C]

I think we're arguing semantics. The sound wave and pressure wave are one in the same (it travels at the speed
of sound in a hot gas).

On a side note: How do you get into in this forum? I got here by accident. I don't see any header in the main page
that gets back. What the hell?

[Matt C]

Never mind, I figured it out by disecting the URL and working backwards. LOL what a dummy

[Admiral Akbar]

I think we're arguing semantics. The sound wave and pressure wave are one in the same (it travels at the speed
of sound in a hot gas).

While sound in itself is a pressure wave, it has very little net displacement.. The pressure waves you are discussing in an expansion chamber involve moving a mass and using the inertia of that mass to create large pressure differences.. They do not move at the speed of sound due to the mass and are considerably slower..

You aren't going to bring up "sonic port choke" are you?

Max

[Matt C]

No, not bringing that up.

It's sonic wave tuning then. I've read numerous papers on expansion chamber design and it was always sonic wave
theory they talked about (in depth). Same goes for headers, sonic wave tuning. Sometimes refered to as organ pipe
tuning. It's the speed of sound in a gas (I remember that from one of my ME classes back in the 1970s.
I've burned up allot of brain cells since then. (and yes, Im an old fucker)

[Matt C]

Does acoustic wave sound better to you? They call them that too! They travel at the speed of sound in a gas.

How about this analogy: Youre in a swimming pool, under water (with no earplugs), someone takes a hammer
and strikes this huge metal object under the water. It blows your eardrums out. Does that sound wave have mass?

You tell me, it would hurt like hell. I know that.

That would be the speed of sound in a liquid obviously. But you get the point.

[RideFree]

In the Twin Cam overlap topic there were 2 dyno responses that indicated no measurable performance change when exhausts are wrapped. So that's 2 no change and I found one vehicle dyno indicating a 1 to 2 % perf increase. So basically no change is probably correct as the dyno would pick up the entire systems response to the single change of wrapping the exhaust.

A lot of good information here. The important part is which effect takes precedence in the system. It appears there isn't one because there are probably cancelling effects rather than multiplying effects.

Also the diff between a pressure wave and a sonic or sound wave is frequency. Sound and sonic are delineating frequency ranges where pressure wave is not and thus is frequency independent. A sound or sonic wave is a mechanical wave that induces pressure fluctuations and is sometimes referred to as a pressure wave if you are not interested in specifying its frequency. Molecules move and change pressure in both. As I understand it anyway.

So now onto reversing aging in mice and sub-DNA. Queue Earl's.

[Matt C]

We used to wrap the headers on the boat mainly for safety reasons. I can't say weather or not it
helped or hurt because we ran the same times. It did help when it came to changing plugs or adjusting
valves on a hot motor.

[Admiral Akbar]

No, not bringing that up.

It's sonic wave tuning then. I've read numerous papers on expansion chamber design and it was always sonic wave
theory they talked about (in depth). Same goes for headers, sonic wave tuning. Sometimes referred to as organ pipe
tuning. It's the speed of sound in a gas (I remember that from one of my ME classes back in the 1970s.
I've burned up allot of brain cells since then. (and yes, Im an old "potty mouth! "er)

It's plausible that it could be close to then the speed of sound..

Jennings claimed in a chamber that the wave speed was about 1700 fps.. I could see sound  being that high in a chamber..
His length for a pipe is..

       Eo x Vs
L = ------------
         N

Where
Eo = exhuast open in deg
Vs = 1700 fps
N  = RPM
L  = length inches

If this were a real formula the units would match..

               degrees  x (feet / seconds)                     deg x feet x minute                                                    12 x 60 
inches = ---------------------------------------   =  -----------------------  (moved the divided bys.. )  x  -------------------
                 rev  / minute                                        rev x seconds                                                             360 x 2

None of this stuff equals inches..

The constant to get convert this to inches would be..

1 rev
------
360 degrees

12 inches
---------
1 foot

60 seconds
-----------
1minute.


1
---   = since the wave has to go up and back..
2

And they seem to match..

Is that the speed of sound inside the chamber?  It does seem that they are at least close.. I do expect that the velocities might be different for a 4 stroke since the cylinder emptying is by a piston pushing gasses out (after a short pop off of pressure when the valve opens).. So the flow in a 4 stroke exhaust system is different and has to be slower as it is determined by the movement of the piston..

Max

[Admiral Akbar]

oops

[Admiral Akbar]

double oops

[gordonr]

 "So the flow in a 4 stroke exhaust system is different and has to be slower as it is determined by the movement of the piston "


?

[turboprop]

Good grief. Taste Great/Less Filling, etc, etc.

Would be allot easier to just pass the hat again and have Stroker do another unbiased test.

I would bet a dollar or two that the typical warmed over street bike would not see any discernible difference with wrapped vs non-wrapped pipes.

Of course, I look forward to hearing more about Boyles Law, Blair, Jennings and Atherton.

I hope everyone has a great Christmas.

vr
Ed

[Matt C]

1670 rings a bell but don't quote me, that was 40+ years ago.

We had to design a pipe for a 50cc engine that they had this crude dyno attached to.

The pressure and temperature inside the pipe was a topic that we discussed at some length and we ended up making
a swag based on some (flawed) assumptions. Reason I say that is b/c we ended up having to cutting something like 5mm
out of the belly of the pipe to get (close) the power we were looking for.

Turned out we assumed that the gas was less dense than it really was.

That's about the limit of my pipe design experience. LOL

[Matt C]

No, I think we should leave pipe design to those that do it for a living. Theory is one thing, practical experience
is another.

I could do back to back tests like this too. I doubt we would be able to tell one way or the other.

[Matt C]

"So the flow in a 4 stroke exhaust system is different and has to be slower as it is determined by the movement of the piston "
?

No, its the same stuff, only a different application.

[Matt C]

Jennings was brilliant!

[gordonr]

Good grief. Taste Great/Less Filling, etc, etc.

Would be allot easier to just pass the hat again and have Stroker do another unbiased test.

I would bet a dollar or two that the typical warmed over street bike would not see any discernible difference with wrapped vs non-wrapped pipes.

Of course, I look forward to hearing more about Boyles Law, Blair, Jennings and Atherton.

I hope everyone has a great Christmas.

vr
Ed

Merry Christmas!

[Admiral Akbar]

"So the flow in a 4 stroke exhaust system is different and has to be slower as it is determined by the movement of the piston "
?

Few things.. The exhaust port on a 2 stoke is way larger, flows way more than a 4 stroke as does the pipe and it's duration is way less as a result it relies wave energy more than mass flow energy.. 

Max

[RideFree]

"So the flow in a 4 stroke exhaust system is different and has to be slower as it is determined by the movement of the piston "
?

Few things.. The exhaust port on a 2 stoke is way larger, flows way more than a 4 stroke as does the pipe and it's duration is way less as a result it relies wave energy more than mass flow energy.. 

Max

Can anyone say expansion chamber. Have a couple on my '70 Yamaha R5 350. They work good.

[Admiral Akbar]

"So the flow in a 4 stroke exhaust system is different and has to be slower as it is determined by the movement of the piston "
?

Few things.. The exhaust port on a 2 stoke is way larger, flows way more than a 4 stroke as does the pipe and it's duration is way less as a result it relies wave energy more than mass flow energy.. 

Max

Can anyone say expansion chamber. Have a couple on my '70 Yamaha R5 350. They work good.

So did my Suzuki X6 club racer..

Max

[strokerjlk]

Good grief. Taste Great/Less Filling, etc, etc.

Would be allot easier to just pass the hat again and have Stroker do another unbiased test.

I would bet a dollar or two that the typical warmed over street bike would not see any discernible difference with wrapped vs non-wrapped pipes.

Of course, I look forward to hearing more about Boyles Law, Blair, Jennings and Atherton.

I hope everyone has a great Christmas.

vr
Ed

Merry Christmas!

wrapping a zilla on my mild 106 didnt change power.
my race bike is wrapped just because it is cooler . 2" drag pipes . if it would increase power I would unwrap them.
merry Christmas 

[gordonr]

"So the flow in a 4 stroke exhaust system is different and has to be slower as it is determined by the movement of the piston "


?

I need a breathalyzer for this computer!       Had to much Christmas cheer last night. Sorry I didn't catch the 2 stroke references.

[Hillside Motorcycle]

We never saw anything on our AHDRA Mod Class racer when we wrapped them, and ended up taking that stuff off, as we were not going to tote the extra weight up the 1320' hill.
Dyno or ET slip showed nada.
Scott