Fluid dynamics and muffler sound

Thank you very much, metalshapes. I'm gonna get a copy.

 

Not like i know anything about exhaust...

but

I think your cam, compression, the volume of air flowing through the motor, and the size, length and thickness of the exhaust tubing has a bunch to do with the sound of your exhaust.
The opening and closing of the valves.. or duration and the position that the cylinders operate in a static order... therefore creating a "pulse" of hot exhaust fumes into the exhaust pipes at certain times in the cycle. These pulses operate like sound waves and can be "tuned" by varying the length of the exhaust tube and diameter. (i know most everyone knows this stuff) well the positive pulse equates to a reflection .. or a reflective pulse because of the push out of the pipe makes the atmospereic pressure push back to fill the void. I beleive that the "rap" sound that you hear.. that "cackle" is the snap of the pressure moving back and forth vibrating the tail pipes along with the atmosphere... maybe. It may be multiple pulses and reflections (from the multiple cylinders) both positive and negative slightly out of sync with each other.
or something.

anyway, a book i have that talks about crank angle and adiabatic expansion and all kinds of crap i dont understand gives a formula which may help you out in your study of exhaust.

The time it takes for the pulse to travel down the length of the pipe

T=L/6Vs ("T" equals "L" divided by 6 times "V" sub "s")

T= time
L= length of the pipe in inches
6 = (some freaky number)
Vs velocity of sound in the air at the temperature and pressure in the induction manifold (roughly 1,100 ft per second)

Now they go on to convert it all to crank angle degrees and look at harvesting horsepower out of each stroke by shortening or lengthening the exhaust. yadd yadd yadd.. i usually fall asleep there.

the book is called "The Sports Car" By Colin Campbell.. who was a hot shot mechanical engineer with a couple masters degrees. It was a book from the 60's and covered mostly euro trash 4 bangers.. but still the designs and principles all equate.

and there are new versions available for purchase online..
http://www.bentleypublishers.com/product.htm?code=x158

Hope this helps in your quest

 

Thank you very much, metalshapes!

I just got a copy of the book, and Chapter 3 is all about sound. It's exactly the kind of inormation that I was looking for when I started this thread.

 

Cool!

I'm glad I could help...

 

And Chapter 6 is all about muffler (silencer) design, which is even better!

 

I bought mine when I was about 13 or 15...
Its one of those books that I will use to look something up, or re read when I need to freshen up some information.
I think its about time again, thanks for making me grab it off the shelf...