Making a 12" Cone Engineering exhaust quieter?

[briandk]

I love the look of my short Cone Engineering reverse megaphone, but the police here has recently started cracking down hard on noisy exhausts and it's honestly quite loud.
Cone Engineering sells their "Quieter Core" exhaust, but it's 18" and not the look I would prefer. Does anyone have any experience fabricating an insert or otherwise quieting the straight through C.E. mufflers? It's mounted on a Mac 2-1 exhaust with a junction right behind the muffler mount, else I would probably have tried a db-killer insert in the header.

 

[Rat_ranger]

Maybe get a tube and make a db killer that sticks into the muffler? Insert in headpipe, but pointing into the muffler. Could be as simple as a piece of tube slipped inside the headpipe with holes drilled in it and a washer welded on the end. Then you could "tune" it by adding holes and opening the hole in the washer. That's basically how the removable baffle on most aftermarket exhausts are.

 

[teazer]

Good idea. The other way is to buy a length of 1" diameter perforated tube and fabricate a new end plate to fit over that tube but hidden just inside the cone so it's less obvious and stuff the gap with two stroke muffle packing. But that's even more work.

Or create a real muffler to fit inside that core with two overlapping tubes - one from the motor side and one towards the outlet. To get it even quieter, block off the ends of both tubes and add enough holes to the end of each pipe for gas to flow through. The combined cross sectional area of those holes should be equal to the area of the tubes you used.

 

[irk miller]

I've used stainless screens you buy for sink drains.

 

[teazer]

Hadn't thought about using one as a baffle screen. I have bough different diameter perf tube to make 2 stroke mufflers out of.

a cheap insert (db killer) or that sink screen might be a better place to start.

 

[DesmoDog]

Yeah... there's a reason all the stock mufflers you see are so big. There is no secret way to quiet things down with a short muffler aside from adding restriction. In the automotive world the rule of thumb is if you want a quiet exhaust you need ten times the engine displacment in the mufflers. So for a one liter engine you'd want ten liters of mufflers. I designed OEM auto mufflers for a lot of years and the smallest I recall was about 6:1 on some truck I've since forgotten.

That said, a smaller diameter perfed pipe with a lot of fiberglass packing around the outside of it is better than a larger one with less packing. You want the packing to be at least .75" thick and you want as much open area in the perfs as you can get. Stainless packing doesn't attenuate nearly as well as fiberglass or basalt, though it is more durable. But that just means it works a lot worse for a lot longer. The inner pipe doesn't need to be louvered but if it is the louvers do NOT have to go into the flow, that's not how sound works. But with short mufflers there's only so much you can do without stuffing something into them and blocking the flow.

 

[trek97]

The internals of a 400F exhaust.
Similar to the CB360. I cut one open and didn't take any pics. Argh!
It was full of smaller pipes and plates welded inside w a fiberglass covered baffle at the end. Like shown in this pic.
the baffles in my Supertrapps run the full length. And wrapped them the "Muffpack kit from steelwooldirect.com
I think you could do something similar pretty easily.
I love the deeper tone of Supertrapps and as quiet or quieter than the dual high pipes Coneengineering.com "quietcore"s I have on my 360.

Supertrapp baffle w ss screen, ss wool and fiberglass mat packing. steelwooldirect.com

Dual Coneengineering quite core's on high pipes.

 

[gt alex]

EMPI make a supertrapp disk baffle/flame arrestor they sell on ebay I say start with 4 baffles and add baffles to reduce back pressure make louder, I have used a spring loaded valve on the cap to stop back pressure spiking at high rpm and it worked very well noise doesn't suddenly erupt and it does help power and sound quality.
I also ran a two barrel (made with 2x 1", 5" long pipes) db kill under the empi style (I made mine next time I'm buying one)) flame arrestor, this was fitted to a 12" long 2" bore glass packed muffler. result can be tuned as low as 94 dba at 4500rpm on a sv650 or a louder if you like

 

[briandk]

I tried something like the supertrap baffle that trek97 posted. It sits mostly in the actual muffler and does cut the noise down a lot, but not quite enough to make it mistakable for a legal can. I got a few different options on the way from ebay and will give those a try, else I might give in and get the quiter-core, though I love how the 12" looks now.

 

[gt alex]

The supertrapp alone needs to be too restrictive to bring the noise down near legal with the 12"
But I am running a 12" with the combo of a double size free flow dbkiller and that is very acceptable. 3discs boarder line legal measured with a meter. but I was worried that was going to choke the top end so it i was running 4 and since advancing the ignition timing, which made the engine much quieter i have gone to 6 and it is not loud.