Mid pipe question
TECH SAVANT
Joined: Dec 2006
Posts: 10,937
From: Saint Augustine, FL
The first thing that must be understood is that the exhaust flow is not a homogeneous constant flow of gases--it IS a series of pulses that occur at a frequency that is always 1/2 the engine speed (in a 4-stroke/cycle engine).
For our engines the fundamental frequencies range from 6.25Hz at idle to 50.0Hz at 6000 RPM--added to this cacophony are overtones and undertones (upper and lower harmonics), and that the initial exhaust velocity is generally ultrasonic at most engine speeds
What follows is a simplified overview of the fluid dynamics involved, with a lot left out, so please no "but what-about" replies...
A resonator is just what the name implies, it is a resonant chamber that at some frequencies of exhaust pulse will do nothing except slow down the pulse as it enters the chamber, restructure it and then send it on it's way through the smaller hole at t'other end--however at certain "resonant" frequencies it will either enhance or inhibit the velocity (and therefore alter the frequency and harmonics) of the exhaust pulse--this is the "tuned" part.
All chambers that are larger then the exhaust pipe ID will have these resonant and non-resonant frequencies, that's why changing cats/mufflers/resonators and even X and H-pipes with different crossover styles will change the character of the sound. Baffles, perforated inner pipes, and the like in mufflers and resonators further alter the sonic characteristics of each component and ultimately the system as a whole.
So in general, unless you know a bit about fluid dynamics and how various exhaust components interact or like to experiment, it is best to stick with all components from a reputable manufacturer. And selected from a particular "line" within their offerings, as they will have done the engineering to make sure each piece works together nicely.
This is also why the conventional wisdom is that you use chambered mufflers with H-pipes and straight-through mufflers with X-pipes. The fluid flow/sonic characteristics of each blend better with each type of muffler.
For our engines the fundamental frequencies range from 6.25Hz at idle to 50.0Hz at 6000 RPM--added to this cacophony are overtones and undertones (upper and lower harmonics), and that the initial exhaust velocity is generally ultrasonic at most engine speeds
What follows is a simplified overview of the fluid dynamics involved, with a lot left out, so please no "but what-about" replies...
A resonator is just what the name implies, it is a resonant chamber that at some frequencies of exhaust pulse will do nothing except slow down the pulse as it enters the chamber, restructure it and then send it on it's way through the smaller hole at t'other end--however at certain "resonant" frequencies it will either enhance or inhibit the velocity (and therefore alter the frequency and harmonics) of the exhaust pulse--this is the "tuned" part.
All chambers that are larger then the exhaust pipe ID will have these resonant and non-resonant frequencies, that's why changing cats/mufflers/resonators and even X and H-pipes with different crossover styles will change the character of the sound. Baffles, perforated inner pipes, and the like in mufflers and resonators further alter the sonic characteristics of each component and ultimately the system as a whole.
So in general, unless you know a bit about fluid dynamics and how various exhaust components interact or like to experiment, it is best to stick with all components from a reputable manufacturer. And selected from a particular "line" within their offerings, as they will have done the engineering to make sure each piece works together nicely.
This is also why the conventional wisdom is that you use chambered mufflers with H-pipes and straight-through mufflers with X-pipes. The fluid flow/sonic characteristics of each blend better with each type of muffler.
4th Gear Member
Joined: Jun 2010
Posts: 1,452
From: TEXAS
The first thing that must be understood is that the exhaust flow is not a homogeneous constant flow of gases--it IS a series of pulses that occur at a frequency that is always 1/2 the engine speed (in a 4-stroke/cycle engine).
For our engines the fundamental frequencies range from 6.25Hz at idle to 50.0Hz at 6000 RPM--added to this cacophony are overtones and undertones (upper and lower harmonics), and that the initial exhaust velocity is generally ultrasonic at most engine speeds
What follows is a simplified overview of the fluid dynamics involved, with a lot left out, so please no "but what-about" replies...
A resonator is just what the name implies, it is a resonant chamber that at some frequencies of exhaust pulse will do nothing except slow down the pulse as it enters the chamber, restructure it and then send it on it's way through the smaller hole at t'other end--however at certain "resonant" frequencies it will either enhance or inhibit the velocity (and therefore alter the frequency and harmonics) of the exhaust pulse--this is the "tuned" part.
All chambers that are larger then the exhaust pipe ID will have these resonant and non-resonant frequencies, that's why changing cats/mufflers/resonators and even X and H-pipes with different crossover styles will change the character of the sound. Baffles, perforated inner pipes, and the like in mufflers and resonators further alter the sonic characteristics of each component and ultimately the system as a whole.
So in general, unless you know a bit about fluid dynamics and how various exhaust components interact or like to experiment, it is best to stick with all components from a reputable manufacturer. And selected from a particular "line" within their offerings, as they will have done the engineering to make sure each piece works together nicely.
This is also why the conventional wisdom is that you use chambered mufflers with H-pipes and straight-through mufflers with X-pipes. The fluid flow/sonic characteristics of each blend better with each type of muffler.
For our engines the fundamental frequencies range from 6.25Hz at idle to 50.0Hz at 6000 RPM--added to this cacophony are overtones and undertones (upper and lower harmonics), and that the initial exhaust velocity is generally ultrasonic at most engine speeds
What follows is a simplified overview of the fluid dynamics involved, with a lot left out, so please no "but what-about" replies...
A resonator is just what the name implies, it is a resonant chamber that at some frequencies of exhaust pulse will do nothing except slow down the pulse as it enters the chamber, restructure it and then send it on it's way through the smaller hole at t'other end--however at certain "resonant" frequencies it will either enhance or inhibit the velocity (and therefore alter the frequency and harmonics) of the exhaust pulse--this is the "tuned" part.
All chambers that are larger then the exhaust pipe ID will have these resonant and non-resonant frequencies, that's why changing cats/mufflers/resonators and even X and H-pipes with different crossover styles will change the character of the sound. Baffles, perforated inner pipes, and the like in mufflers and resonators further alter the sonic characteristics of each component and ultimately the system as a whole.
So in general, unless you know a bit about fluid dynamics and how various exhaust components interact or like to experiment, it is best to stick with all components from a reputable manufacturer. And selected from a particular "line" within their offerings, as they will have done the engineering to make sure each piece works together nicely.
This is also why the conventional wisdom is that you use chambered mufflers with H-pipes and straight-through mufflers with X-pipes. The fluid flow/sonic characteristics of each blend better with each type of muffler.
TECH SAVANT
Joined: Dec 2006
Posts: 10,937
From: Saint Augustine, FL
I don't like the sound of o/r X-pipes with almost any muffler--in fact I'm not wild about o/r H or X-pipes at all, just too loud and on a "basic bolt-on" GT are advertising something that the car has no possibility of delivering...
4th Gear Member
Joined: Jun 2010
Posts: 1,452
From: TEXAS
