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View Full Version : Changing the sound of a stock muffler


ff
04-30-2007, 12:47 PM
I'm wondering if it's possible to change the sound of a muffler. The stock muffler on the Si is a bit louder than I would like, and it also resonates a bit too much under throttle at slower highway speeds. It's an unnecessary drone. Is it possible to modify the sound that's emitted by changing the length of the outlet? Or by placing some sort of baffling in the outlet? Would that change the resonant frequency?

I'm just curious.

undefined
04-30-2007, 12:52 PM
sure--here you go

http://www.vroombox.com/vroombox/

ff
04-30-2007, 12:55 PM
sure--here you go

http://www.vroombox.com/vroombox/

VroomBox utilizes a powerful microprocessor to digitally recreate the sound of 15 different cars and fantasy vehicles, and play them through speakers under the car. It even includes special effects such as screeching tires and turbo blow-off valves that trigger automatically.

:lol: I can think of some fun uses for that...

John V
04-30-2007, 03:07 PM
I'm wondering if it's possible to change the sound of a muffler. The stock muffler on the Si is a bit louder than I would like, and it also resonates a bit too much under throttle at slower highway speeds. It's an unnecessary drone. Is it possible to modify the sound that's emitted by changing the length of the outlet? Or by placing some sort of baffling in the outlet? Would that change the resonant frequency?

I'm just curious.

At what RPM does the resonance occur?

If you know, you can calculate the engine firing rate (EFR) and insert a small helmholtz resonator (with a length of a quarter wavelength) in parallel with the exhaust after the cat. Mustang guys do this all the time to eliminate an EFR generated resonance with aftermarket muffler systems.

FYI the S2000 has one of these resonators in its exhaust system. Cars frequently have them on the intake pipe or airbox as well. It looks like a piece of pipe (or plastic chamber) which sticks off the side of the exhaust (or intake).

You can see an example in this exhaust - it's sticking out perpendicular to the pipe on the far end of this image.

http://www.honda.co.jp/ACCESS/automobiles/s2000/images/modulo/muffler.jpg

Plaz
04-30-2007, 03:40 PM
http://www1.istockphoto.com/file_thumbview_approve/1366733/2/istockphoto_1366733_white_socks.jpg

ff
04-30-2007, 04:09 PM
At what RPM does the resonance occur?

I'll have to pay closer attention the next time I drive it. There's actually two different times when I notice the resonance. The one from the exhaust actually occurs over a range of lower RPMs, which I don't like (though I'm sure the ricers do, and this is why Honda did it). Another occurs from the intake for a brief moment at high RPMs. I followed the intake tube, and it's pulling all of its air directly from the inside of the left fender, which probably helps amplify the engine note at higher RPMs. It does sound pretty nice at WOT, but personally, I don't believe it needs to be as loud as it is.

I wonder what would happen if I simply removed the intake from the entrance to the fender, and allowed it to draw air from the front of the engine bay... it would be an easy test to try out.

Hey, thanks for the tip on the helmholtz resonator deal. I think that I'll ask around some of the muffler shops in the area, and see if anyone knows what one is.

http://www1.istockphoto.com/file_thumbview_approve/1366733/2/istockphoto_1366733_white_socks.jpg
There's more than 2 uses for a pair of socks? Who wouldda thunk it...

lemming
05-13-2007, 05:54 PM
isn't an aftermarket muffler pretty cheap?

or does it hafta remain "stock" for appearances

ff
05-14-2007, 09:00 AM
isn't an aftermarket muffler pretty cheap?

or does it hafta remain "stock" for appearances

The aftermarket ones I've seen are all > $500, and seem like they make the exhaust as loud or louder. Granted, I haven't done too much snooping around. I'd prefer to keep the look "stock", so I'm going to start by seeing if the muffler from the EX will bolt on (eBay...). I happen to have an appointment at the dealer today for my free oil change, so I'll ask questions then (and most likely get a bunch of blank stares).

DamnYank!
05-22-2007, 02:48 AM
changing the outlet/tip length and diameter will affect sound, but i can't say exactly what you would need to change in order to get the results you want. additionally, a tip/extension that is resonated can also help reduce the symptoms you are having.

operknockity
05-22-2007, 03:56 AM
...

ff
05-22-2007, 09:06 AM
changing the outlet/tip length and diameter will affect sound, but i can't say exactly what you would need to change in order to get the results you want. additionally, a tip/extension that is resonated can also help reduce the symptoms you are having.

I hadn't thought of changing the tip. I did some quick searching on google, and there are tips that will change exhaust sound. So I'm going to start by taking the stock tip off, and see where I stand then. That should be a considerably cheaper and easier starting point.

BTW, I did ask the dealer about swapping out the muffler with one on an EX (or other), and as expected, just got a blank stare ("I have no idea what you're talking about.... but can I interest you in our $199 detailing and body protection package?"). They were unwilling to do any checking or asking around. Even the parts manager just threw her arms up in confusion, and sent me packing. :rolleyes: