Factors influencing exhaust sound?

In looking for cat back exhaust systems, are there rules of thumb to predict sound volume and tone?

Seems like the common variables are:

pipe size, with 3" most desirable for flow- louder and deeper sound?

volume in cans- larger equals more potential 'muffling'? ,

outlet size and number (dual vs quad)- difference in tone?

packing of muffler: much variation here?

offset of inlet to outlet in muffler-does that make a predictable difference?

presence or absence of resonator in mid pipe- does this change tone or volume more?

What else?

From what I've read here it seems the mufflers make the largest difference. Pipe diameter and resonators not so much. I know that doesn't answer all of your questions. Hopefully other with more detailed knowledge will chime in.

Adding a straight through muffler mid pipe as a resonator seems to change things up as well.

Muffler packing quality seems to make a good bit of difference as well.

Good rule of thumb is that an efficient muffler allows the peak and troughs of pressure to flatten out, and temperature to decrease, which reduces noise volume. That also allows the same amount of gas to flow through smaller piping. Therefore going from smaller to larger diameter as the gas moves away from the turbo is really pointless. Putting a 3" on a 2.5" downpipe is pointless and gains nothing.

Muffler efficiency is reduced a lot with the section of the piping in and out and through the muffler. Meaning, a 3" muffler the same size as a 2" muffler will be louder, even when both designs are as well optimized as possible. This is why many cars are fitted with a Y-pipe and two mufflers. To get the same final noise volume from a 3" muffler as the 2" item it's internal volume has to be larger. Iron rule.

Tips that have a larger total cross-sectional area than the pipe into the muffler are a good example and actually increase noise. IOW a 3" midpipe has an area of 7.07in2. Regardless of how many mufflers or tips there are they do not need a total area greater than this.

Tips that increase in diameter works like a megaphone. Those cool looking tips that go from 2" from the muffler to 4" at the outlet are making the exhaust louder again, after the mufflers cut the noise.

Too bad this look is so damn fashionable!

Straight-through mufflers and resonators are usually a Burgess type muffler, also called absorption type or glass-pack. These do not really reduce noise volume that much, but are very good at cutting higher frequencies which certainly attract more attention. Remember your ears do not hear every frequency equally. Shifting the pitch of the noise lower makes that noise less objectionable or easily locatable. Good strategy if your exhaust note is too raspy for your taste.

Hope this helps.

Good rule of thumb is that an efficient muffler allows the peak and troughs of pressure to flatten out, and temperature to decrease, which reduces noise volume. That also allows the same amount of gas to flow through smaller piping. Therefore going from smaller to larger diameter as the gas moves away from the turbo is really pointless. Putting a 3" on a 2.5" downpipe is pointless and gains nothing.

 

Muffler efficiency is reduced a lot with the section of the piping in and out and through the muffler. Meaning, a 3" muffler the same size as a 2" muffler will be louder, even when both designs are as well optimized as possible. This is why many cars are fitted with a Y-pipe and two mufflers. To get the same final noise volume from a 3" muffler as the 2" item it's internal volume has to be larger. Iron rule.

 

Tips that have a larger total cross-sectional area than the pipe into the muffler are a good example and actually increase noise. IOW a 3" midpipe has an area of 7.07in2. Regardless of how many mufflers or tips there are they do not need a total area greater than this.

Tips that increase in diameter works like a megaphone. Those cool looking tips that go from 2" from the muffler to 4" at the outlet are making the exhaust louder again, after the mufflers cut the noise.

 

Too bad this look is so damn fashionable!

 

Straight-through mufflers and resonators are usually a Burgess type muffler, also called absorption type or glass-pack. These do not really reduce noise volume that much, but are very good at cutting higher frequencies which certainly attract more attention. Remember your ears do not hear every frequency equally. Shifting the pitch of the noise lower makes that noise less objectionable or easily locatable. Good strategy if your exhaust note is too raspy for your taste.

 

Hope this helps.

how do you take out the rasp? i have 3" downpipe into glasspack and was split into 2.5" duals but didn't know if i should change it and to what? what is your option on single 3" or dual 3"?

Run a catted down pipe or add resonator to get rid of rasp.

Already running a 24" glasspack as a resonator