Exhaust flow vs sound question

This is a key question in my study of Ferrari exhaust systems.
Both "A" and "B" have equal size muffler bodies with the same volume of absorptive packing (represented by the tan color).
"A" has a 2.5" tube which splits into two smaller tubes throughout to the resonated tailpipes
"B" has a 2.5" pipe throughout before splitting to twin resonated tailpipes

What is the difference in sound (and flow) between the two systems?

Many thanks
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Rus,

You'll have a master's degree in exhaust design if you keep this up!!!

It's simple physics in "A". If you increase the volume you decrease the pressure. You have twice the amount of piope for the same amount of exhaust gases. So, there is less flow resistance.

Also, you are increasing the area of silencing by addressing more damping material to the gas flow.

So, "A" would be a better way to create better sound quality with reduced flow resistance.

The downside is that it is a more expensive muffler to make, it would be a bit heavier, but I would prefer it. Remember that weight is always a consideration of muffler design.

 

Did you know how a 355 stock muffler looks like inside?

 

I would think a lot of it depends on the size of the pipes going through the mufflers. What would the total surface area of the single pipe be compared to the dual pipes?

 

As far as the area of the pipes, the 2.5" pipe in "B" has a cross sectional area of about 4.91 square inches prior to the resonator split.

In "A", a 2.5" single pipe dumps into twin 2.25" pipes with cross sectional areas of 3.97 sq. in each, or a total cross sectional area of 7.94 sq. in.

There will be more surface area of pipe exposed to the boundry layer flow to produce drag, but in this instance I do not think it will signifigantly affect total flow resistance with the large increase in cross sectional area (and decreased total flow resistance). It does allow as Greg says more surface area presented for sound absorbtion.

This efficiency in sound absorbtion is important in a mid-transverse V-8 application as there is limited room to begin with, and this maximizes the silencing from constrained size absorptive muffler while keeping flow resistance low. Many other acoustic box non-absorptive mufflers have to add restrictive passages and chambers to reduce sound and thereby add resistance. While primitive (like me) and not entirely accurate I understand, I am intuitively attracted the "roll a golf ball end-to-end" school of exhaust design common to absorptive silencers and not so much with chambered mufflers although they work well.

That is also why there are two mufflers illustrated instead of one large one. As Greg has pointed out and I have read in some exhaust texts, the volume effect is not linear. Theoretically, two mufflers of volume "V" are more effective than one muffler of volume 2V - i.e. "dual resonant silencing".

Studying older Ferrari exhaust systems from the earliest 250 through 365 series, almost all had some variant of "A", some with as many as 4 mufflers per side as on the GTC/4 and 400 series. The exhaust must have been very heavy, but these are also about the best sounding street Ferraris.

I'm still very interested in folk's actual experience and opinions about "A" and "B" comparatively and the different tonal qualities they produce ( high or low, harsh vs smooth) as I cannot find as much about this. All comments and advice welcome - thanks!

 

Russ,
definitely A is a better flowing muffler set up than B and I believe the sound attenuation would also be better than B.

 

I havnt seen anything yet, but outside of a stainless Tubi, Stebro. Larini, etc.. Why hasnt anyone built a muffler in simular construction to a motorcycle. What I am refering to is like the type you see on performance street bikes with carbon fiber shells, and riveted on stainless end caps.

What if it went a step father. All stainless, but the main muffler section was able to be opened in some way. The outer shell could be like a clam shell, or wrapper perhaps, with individual ends where the inlet and outlet pipes attach, and the internals could be relocated or internal routing altered, or different pipes or baffles added or deleted, as well as packing, for sound quality and engine performance. You could then tune the muffler to your own tastes in sound and performance quality, instead of being stuck with a too loud or too quiet "one part fits all" muffler that offers no real performance gain.

 

More sq inch pipe than (HorsePower/52)Sq Inch does not result in more Hp but it sure results in more noise, because of the lower flow speed.
Damping becomes less effective when the air speed goes down.