A tuned exhaust system and speaker enclosure have a lot in common. In a tuned labyrinth speaker enclosure (ported) when the speaker moves forward a sound wave travels from the rear of the speaker as well as the front. When this sound wave reaches the end of the labyrinth or port it causes a reverse wave (rarefaction) to travel back through the labyrinth and slam into the back of the speaker to stop it where it started (speaker damping). The tuned frequency is determined by the length of the labyrinth.
An exhaust system is not too different. The pipes combined with the back & forth flow through the muffler is a tuned labyrinth. Desired back pressure is determined by the frequency at which the system is tuned. Back pressure is not created by restriction but by a properly tuned system. Modifications to an exhaust system can drastically change the desired back pressure.

 

AGNAV93, is that you?

If or if not, interesting read none the less.

DUCK

 

 

Yep. I think they call the basic concept a Helmholtz tuned resonator. You're basically blowing over the top of a pop bottle. It will have a resonant frequency and a bunch of harmonics above it depending on the shape and size of the chambers. Just like in various brass instruments, this gives it a characteristic sound. The 'spectrum' of flow for the exhaust works in concert with the engine and intake system to give a torque curve. Change one part and you change the curve - for better or worse.

 

In the words of Jay-Z

"Jigga what"

--Joe

 

Lost me on this one. I think you are confusing sound waves with hot gasses flowing through a pipe. The sound waves will go backwards but there is positive flow through the exhaust system at all times the engine is running. Put your hand against your tailpipe and feel the flow. There are pulses but never will your hand get sucked into the exhaust pipe.

 

JimmyJoe- you've made a good point. Anyone who has launched a boat and had their exhaust pipe go underwater knows that water won't get sucked into the pipe.

Dennis- Counterpoint?

 

I believe that a pressure pulse can travel against the flow.

Also, in this muffler both inlet pipes flow straight through the muffler and open into the rear crossover chamber. With the firing order alternating between banks you will have low pressure on one side and high pressure on the other, then reversed as a cylinder in the other bank fires as the pressure tries to equalize between banks. There will always be a positive pressure in the entire system and never a vacuum, just some pressure waves bouncing back & forth that really aren't affected by the directional flow of gases.

 

I believe that a relative pressure differential can travel against the flow, but the distance it could exist would depend on the force of both the wave and the pressure body it moved in. Eventually it would be overtaken by the ambiant flow pressure, but the time/distance variables . . .well. . .would vary too greatly to guestimate.
Your logic seems correct according to what I know of airflow dynamics, though. It's hard to visualize, huh? It's even harder to explain.

JimmyJoe- any thoughts?

 

Any chance of Bose making an exhaust system for the L?

 

Where's Albert Einstein when we need him?

I do like his famous quote though...

"Gravity is not responsible for people falling in love."

 

BaddKharma,

You haven't heard of Bossani?

 

My response to Albert's famous quote would be...

Gravity is a big help for people making love!

 

Oooh! Oooh! Favorite Einstein - attributed quotes:

"Imagination is more important than knowledge."

"Not everything that can be counted counts, and not everything that counts can be counted."