Comments on: Muffler Design

By: Bonkoh

Bonkoh — Sun, 21 Dec 2008 23:20:39 +0000

Does anyone happen to have a copy of that David Vizard exhaust tuning article linked above?

I have managed to read all of it except page 5. If anyone can forward the ‘vizard5.jpg’ image I’d really appreciate it.

bonkoh.2007@gmail.com

By: Julian Edgar

Julian Edgar — Wed, 10 Dec 2008 09:08:23 +0000

I don’t know of any such book. Sorry.

By: Stone

Stone — Wed, 10 Dec 2008 08:32:28 +0000

Hello Julian! I am thinking to build “tailor made” mufflers to serve my customers. Do you recommend any handbook for muffler design? Thank you.

By: Wave

Wave — Mon, 17 Nov 2008 02:17:07 +0000

The idea of huge rear mufflers being used as bumpers and crumple zones has already been put into mass production in the US market, so obviously you guys are on a winner! It’s only been done on very pedestrian cars though, nothing with any pretence to high performance.

By: Geoff Thomasd

Geoff Thomasd — Tue, 08 Apr 2008 13:35:53 +0000

Talking about making your own muffler, I’ve done it. I read some books, look at designs and found nothing like what I made.
The car is my 105 Alfa race car with very tuned 239hp 2L motor. We planed to do 3 tests on the dyno changing from the collector back only.

Test 1
The exhaust consisted of a 2” stainless pipe of about 30 inches into a divergence nozzle expanding to a 3” x 14” straight trough type muffler into a convergence nozzle reducing back down to 2’and then a pipe of about 60 inches with a 30-40deg mandrel bend in the middle. These lengths are not optimized as we just had this stuff lying around This ends behind the front door so the whole system is very short and sounds like a very cranky cat, not very pleasant at all.

Test 2
No exhaust system at all

Test 3
My exhaust system consisted of, well if you could imagine a banana shape with a 2 inch inlet and a 7×3 oval outlet. The internal lining was perforated aluminum shaped to form an oval tapered, curved pipe. The outer covering was made oval and curved from high heat epoxy and fiberglass. The muffling material was just fiber glass wool packed into the void so at the inlet end there was 2 or so inches of wadding and next to nothing at the outlet. It gave a great deep meaty sound which would have been expected due to the density of the materials used in the pipe.

So how did they perform?
Test 1 recorded 239hp
Test 2 added 9 hp but lost torque at 4000 (max torque is at 6000rpm)
Test 3 added 4hp no loss of torque, but me, not being a muffler expert had durability issues. I like every one else thought the epoxy would break down from the heat but the problem was the perforated aluminum expanding and buckling in.

Anyway it was educational.

By: Gigapunk

Gigapunk — Tue, 18 Mar 2008 13:18:38 +0000

Tim,
I love you idea of using the bumbers as chambers! But the notion of under the floor would be dicey just due to the heat. There is great airflow where the are traditionally mounted, and that airflow is (I’m Guessing) a large part of the reason as to why they are there.

By: Tim Paton

Tim Paton — Tue, 11 Mar 2008 10:43:15 +0000

I’ve thought for some time that there is an overlap in basic requirements for exhaust muffling and crash protection.

As we’ve read here, a muffler needs volume, filled with not much at all. A crumple zone needs volume, filled with a bit of crushable structure and not much else.

The bumper bar (or, these days, colour-coded moulded bumper panel) and rear crumple zone of a car are pretty much wasted space. You can’t put the fuel tank there any more, and rear seats (in hatches, third row for wagons and SUVs) have to be set far enough inboard that they won’t get crushed in a rear-ender.

Why not use that space – the under-floor space especially – for an effective large-volume muffler? Why do we waste useful underfloor space further forward with big metal box full of crushable baffles and loosely packed rock-wool? A straight-through exhaust pipe takes much less space than a muffler… the remainder could be used to accommodate deeper foot-wells, under-floor storage compartments, fold-away seats as seen in the (sadly orphaned) Holden Zafira… dare I say, a full-size spare wheel?

Forward-mounted, longitudinally-aligned mufflers are just a silly packaging choice, as far as I can see.

Another crazy idea – has anybody ever played with a Helmholtz resonator muffler system? Helmholtz resonators – effectively an tuned cavity and neck hanging off the side of a pipe or duct – are used extensively on engine intake systems, to eliminate problem frequencies from the induction sound. Exhaust noise is also somewhat tonal… why not hang a set of tuned resonators off the exhaust pipe to attenuate the noise? Again, all it takes is some empty air space, at the back of the car where you need some crumple zones anyway…

By: Mike Figaro

Mike Figaro — Mon, 10 Mar 2008 04:50:17 +0000

Hi guys, chiming in as I found this article researching rear diffusers and also exhaust headers. I am planning on embarking on a design journey to design a new muffler. What occured to me is that volume itself provides a method to expand and damp the energy put forth, but what about selective band pass filtering to a particular exhasut note. The flow master is the best that I have seen attempting to actually create and acoustic chamber as well as providing a pressure vessel that is not restrictive. Why are there not more acoustic designs out there? What conventions have lead us to an oval? The ease of manufacturing? I found the viazrd articles a great read and I appreciate the post. I look forward to experiment on my I6 IS300.
Julian, if you ever need some replacemen thood props, give me a ring.

Mike Figaro

By: Julian Edgar

Julian Edgar — Fri, 07 Mar 2008 22:57:33 +0000

My Lexus LS400, with two main rear mufflers and others further forward (include the cat converters as they also act as mufflers) would have had a total volume (I’d guess) of ~60 litres. Incidentally, it’s the volume as a whole of the muffler, so just the external measurements minus wall thickneses.

In the past when we’ve tested mufflers, with all other aspects being the same, the larger their volume, the better they work at muffling.

By: Craig Dunn

Craig Dunn — Fri, 07 Mar 2008 09:55:08 +0000

According to the article, muffler volume changes effect the ‘low’ frequency sounds, and 14ci is required for every Max hp. ths works out at 23 litres muffler capacity for every 100hp. As such a commodore or falcon would therefore require 60 litres of mufflers capacity for this rule of thumb.(not including the spce required for any glassfibres etc). This seems to me to be a large space to find under a car, and i am sure that most car mufflers do not have that capacity. Just from looking at the mufflers, it seems to me that ‘luxury’ cars like lexus etc that are quiet have really large mufflers whereas ’sporty’ cars that are noisier like porsche a have smaller muffler capacity. So although the capacity of a lexus muffler def is not 60+ litres it appears that the larger the muffler capacity the greater the noise drop. I wonder if the relation is linear (i.e if i add 1 more muffler to my existing 2 muffler system the noise will be 2/3 of the existing, or if pipe characteristics or pressures play a role. i am sure this could be worked out mathmatically and by experimentation?
thanks . Craig