[dunc2027]

The general rule of thumb for mufflers (of the same type ) is bigger = quieter. However, most people say dual exhaust is louder (I'm assuming the same mufflers in either case, just one vs two). I'm somewhat confused, because the way I see it, you're pushing half the amount of air through the same muffler size, so it's the same thing doubling the muffler size. So why is it louder?

More practically: Two mufflers in series would obviously be quieter (twice as?) than one, but restrict twice as much. What about two in parallel? Would they restrict both flow and volume half as much? What about quads, having a Y with each leg having back-to-back mufflers?

 

[cerial]

Ok you need to think of a exhaust system like it was full of water and your engine was a pump.

The pulses will "stick to" the insides of the pipe where as the air/sound in the middle is allowed to flow through.

The muffler (in general) creates a restriction diverting and cancling sound.

Maybe this will help;

Because more sound hits the sides of duals that sound hitting the sides makes them louder.

 

[dunc2027]

Ah, that makes sense. I have read some about mufflers and agree that they work mostly by cancellation (by various methods). I had considered turbulence in general (particularly from bends), but really hadn't thought about friction (especially in a straight pipe!). A little Google-fu tells me drag forces are proportional to the square of velocity, so the "4 times speed means 16 times friction" also makes sense. Thanks for the info.

I don't know how to apply that to my question about quad mufflers, though. Plus, if the quad system is the same diameter as the single system, air velocity is lower and therefore friction is lower. I would guess that overall resistance would be the same. Any idea if the volume would be different?

 

[BOOT77]

Some mufflers flow better than others. What do you want quiet or max power? The exhaust flows in pulses and that's why a H or X pipe can help, it lets each pulse see two mufflers.

High flow mufflers are loud. A perforated straight tube(not louvered like a cherry bomb) can flow more than a straight pipe because it has less surface friction area.

Two pipes with equal area of one larger pipe, have more surface area and also weight more. I like a Y-pipe with a single high flow muffler if the single pipe size is practical to route. Otherwise duals with two high flow muffler and no X or H.

 

[BOOT77]

Also quad mufflers were tried long ago before X & H pipes, 4 are heavier and cost more, plus take up more room.

 

[dunc2027]

I don't have a specific goal in mind, just playing the what-if game. That makes sense about the perforations. I swear I've read that bit about H/X and pulses before -- amazing how much we take in and forget.

In some cases there will already only be one pipe, like an inline six. If I limit my choices to one muffler or a quad Y of the same mufflers, how will the resistance and volume compare?

 

[BogiesAnnex1]

One of the points of the H pipe is to mellow out the bark of duals on a V8’s system. An interesting thing is an X pipe sharpens the bark in frequency. While generally conceded that an X crossover usually results in a better and higher power profile it tends to be screechy in tone and louder. This probably speaks to the right angles and added distances of an H pipe are removing energy from the exhaust stream and changing or mixing the cadence across the cylinder banks.

You have to be careful with the volumes, David Vizard touches on this in several of his books. At least from the standpoint of a competition engine you can improve or upset the scavenging of a header system with mufflers depending on how much volume they have and their distance from the collector to where they are placed. Things that work on single or twin cylinder, in some cases even inline fours do not work on multiple cylinder V configurations engines megaphones being a classic example.

Bogie