Exhaust Wraps versus Performance

[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