Big Blue: The questions that you ask are or could be complicated if an exact answer is required. There are some hairy Stochastic calculations that would require evaluating; possibly using thermal expansion graphs and velocity/viscosity coefficients.
That being said there are several theories and applications that you can refer to to answer your questions.
Here is what I know (I think):
With respect to scavenging the expended gasses of combustion (from the valve seats to the pipe end). For a given exhaust geometry ; the further back (rearward) on the exhaust pipe a muffler is placed the air column within the pipe will be more "reactive" . Tending to be more restrictive. This could occur or have greater effect at various points in the engine's power band.
The only reason that a less restrictive exhaust system "allows" more power to be generated at the motor is that there would be less resistance AND reactance to the transmission of the gaseous impulse generated at the piston. Doing so for a given geometry "would tend" to be more restrictive to the gaseous mass's velocity occurring at the input to the system. (Allows less power). This occurs because instead of acting as a transmission line [resistive impedance] the cavity volume of the total length of the pipe(pre muffler) comes into play{TT*r^2 x L}. This cavity behaves or has a "springy" characteristic in attempting to push the gaseous impulse backward into the valve cavity (Cylinder Valve). This would reduce the effective cavity volume of the cylinder upon opening at the intake (compressing)stroke. It would be assumed that having a larger pipe would be less restrictive in this geometry, but look at the formula in placing the values for the different size pipeage 2, 2.25, and 2.5" into that formula that the smaller pipe (within reason) reduces the net volume and lowers the pipe cavity volume. This could be used to "tune" an exhaust system with respect to sound and "flow". Since any work performed by the muffler with respect to the gas impulse has already been performed following the muffler it does little to cause restriction in the system. (within limits)
Now lets move that same muffler forward within the configuration. The air column in the input pipe if small is "usually" less restrictive AND reactive. The majority of the exhaust expansion occurs within the muffler and therefore this allows the gaseous impulse from the exhaust valve to be succepted at a higher rate. This is or would tend to cause a greater "scavenging" effect to the gasses. This is usually why OEM systems for trucks place the muffler either at the mid-point or further "up" into the configuration. The muffler breaks up the cavitation of the exhaust pipe volume allowing better flow.
For sound enthusiasts this permits the "sound" to be lower in level. Making the Exhaust note quieter at some given R/m's. In other words "Louder">> further back(but slightly more restrictive).
This geometry presumes a given muffler volume and porting. Flowmaster's type mufflers "tend" to have low restrictive effects when mounted "up" on the exhaust pipe. The cavity effect of the muffler when coupled with a short, "fat" pipe 2.5-3.0" tends to reduce both the restrictive, and reactive effects of such a system.
This would "tend" to be less restrictive over a greater range of R/m's.
Now considering how a muffler works the gaseous impulse following the muffler has been smoothed significantly from a pulse to wind (within limits) and this volume velocity has been reduced significantly.
The pipe out of the back or side will have less effect on the net restriction of the exhaust system. So dumping the output of the muffler or running a reasonable amount of muffler pipe would "tend" not to have a negative effect on such a system.
>> If you want to increase the net sound output of a given muffler system figure on moving the muffler further back on the exhaust pipe (maybe behind the differential) and shortening the trailer pipe as required. However if you need to pick up some needed hp and torque arrange the system to mounted as far front as possible to the engine or cat's and then dump the muffler outputs as best that can be done. Increase the output diameter of the muffler exhaust pipe by at least 1/4" to 2.5" dia. and drop it behind the differential as desired. It is more important to have as few significant bends in the pipe minimized following the muffler. Or as best as can be done within reason.
However if you have a Navigator or Expedition it would dump the exhaust out the sides behind the wheels.
Entropy Enhancement:
You can pick up a significant improvement an any exhaust system by keeping the net volume of gas as hot as possible before the muffler. Wrapping the exhaust headers , lead pipe with Thermo Tape can improve output and flow by 7-15% on average. Good value improvement.
Paint or coat your headers "Silver" (not the Cat's) and input pipes with good grade Header Paint can also improve the system thermodynamically to give an improvement.
I'm open to discussion if you want. I didn't think I would have posted this long (sorry).
Peaze
Linear Mode
