Mufflers - "one size fits all"?

[H-viken]

There is a lot of talk about varying header size, while mufflers seem to be "one size fits all". Why is that? Why does M&K for example not match their mufflers according to header size?

What am I missing?

/Johan

[McLaren-TAG]

They might fit from a physical standpoint but you're right, they're far from one size fits all from a practical use standpoint.

Research what type of response you want. A lot of people consider sound as the main factor but the torque range can really shift towards the wrong place in the RPM curve if not matched properly.

[H-viken]

Originally Posted by McLaren-TAG

the torque range can really shift towards the wrong place in the RPM curve if not matched properly.

I was thinking along the lines of power. Seems that much of the benefits gained from going up or down in header size will be negated by the muffler.

[J0hnny]

Originally Posted by H-viken

I was thinking along the lines of power. Seems that much of the benefits gained from going up or down in header size will be negated by the muffler.

This really depends on the vehicle and application, for the 911 you a have a very unique situation, the muffler is practically attached to the header, this doesn't happen in other type of vehicles.

A short answer for the original question is, no, one size doesn't fit all, specially in a 911, if the expansion chambers are to big or to small, or the muffler have too much restriction, it will be reflected on the power-band, this is one of the reasons Porsche opted for lengthening the exhaust path in later models.

How exactly the power-band changes will depend on several factors, usually more restrictive mufflers give better low rpm torque and response, while free flowing ones sacrifice some torque and bottom end for top end performance.

Then you have to consider acoustics on top of all that, and it becomes a huge tangled mess, highly entertaining though.

[Bill Verburg]

Originally Posted by H-viken

There is a lot of talk about varying header size, while mufflers seem to be "one size fits all". Why is that? Why does M&K for example not match their mufflers according to header size?

What am I missing?

/Johan

The function of the header and muffler are very different

the header directs the flow of the exhaust gases, it's function is
to contain the heat, hotter gas expands and flows faster
to direct the flow and keep the flow velocity as high as possible
to collect the flow from the separate cylinders in a way that doesn't introduce turbulence
to enhance acoustic reverberation that can be used to enhance cylinder filling and exhaustion

these functions are highly dependent on the geometry of the pipes and collectors, too big a pipe slows flow and allows the gas to cool too quickly, too small a pipe causes pressures to rise also inhibiting flow, too sharp a bend or poorly constructed transition introduces turbulence that slows flow, the length of the pipe and transition designs need to be correct to set up the standing waves used in acoustic tuning to enhance cylinder fill and evacuation.

a muffler on the other hand is designed to slow flow and absorb heat and acoustic energy, this is done by expansion, you want the largest/coolest volume to expand into(atmosphere is the best) and by absorption w/ packing material and by internal reflection.

A muffler can be designed for flow at the expense of acoustic modulation or vice versa, the bigger it is the better it can be at both, There are internal designs that can enhance one or the other property but rarely both

[Reiver]

Exhaust tuning puts your sweet spot where you want it or use the car the most.
Buying a muffler because of the noise it makes does nothing for drivability or performance.
Usually, the more noise it makes on a stock motor just moves your sweet spot (torque band) higher on the rpm scale....making the car less responsive unless at wot.
This is an example of form over function.
If you have a highly modified/rodded 911 then the noise and performance can go together.
Some swear their car is faster with that new, lightweight, noisy muffler but they never dyno the thing thru the rpm band to find out....the 'sound' makes it faster.
BTW, the M&K guy on this site will tell you the same thing, he has on occasion.

[targa44]

Is anyone aware of a successful conversion to (2) separate mufflers for a 3.0 liter? - while keeping the noise to a more stockish level? Are there any specifics on type of mufflers and/or issues?

thanks,

[kach22i]

Originally Posted by targa44

Is anyone aware of a successful conversion to (2) separate mufflers for a 3.0 liter? - while keeping the noise to a more stockish level? Are there any specifics on type of mufflers and/or issues?

thanks,

Several examples and discussion in this old thread:
Custom Exhaust

In general, dual cats and or dual mufflers are said to enhance top end rpm peak performance, while longer header pipe runs and combined exhaust via muffler mixing chamber increases low end torque and street-ability.

In that link someone managed to combine long headers with dual mufflers, then mixed the flows near the end, one of my favorites.

In fact if I recall correctly, there is even an example with electric by-pass baffles for top end performance, which close up and take a longer path to enhance low end performance.

[targa44]

Thank you. That was good stuff.

Food for thought (maybe not much): I too would like to get rid of the rearward weight - and have been tossing around the idea of going forward and using the rear seat area for some individual mufflers. It would involve cutting out the rear seat area and creating a cavity (very well insulated boxed in firewall) to put things. From there, send exhaust down and out just before the rear tires like the american hotrods of old. If needed, create some side openings (ala Boxster) to help get rid of the heat. Well, we can always dream.

[RarlyL8]

The inlets on our mufflers are slightly larger than the stock heat exchanger or SSI outlets that they were designed to be used with. The optimal application is 2.2L to 3.2L. To ring out the last HP on a modified engine requires a lot of attention to the entire exhaust system. Our headers have the same size outlet for the same reason. For the street 911 there is not a ton of performance to be gained from any muffler as there is not much left on the table, you just need a muffler that will facilitate any modifications. What is left to improve on is weight reduction and sound quality. We have reduced weight tremendously through the use of strong light alloys (321 stainless). Our single inlet single outlet muffler for the SC/Carrera weighs 10 pounds. The heaviest of the dual inlet mufflers weighs 15 pounds. Retaining that raspy air cooled howl on the pipe is a bonus.

[H-viken]

Brian,

I have a set of headers on the shelf with 60mm pipes after the collector. What's the inlet size of the M&K mufflers?

/Johan