bike's too loud.... DIY SILENCER INSERT

[McgWRATH5150]

well, today my friend's half deaf 30 year motocross veteran/loud stuff contisure dad told me my bike was too loud... (and i thought it was only my neighbors.) And although I was readily aware of my bike being not trail legal (it is, when you can outrun the rangers:lol:?) but on a more legal note, I searched for hours to find an insert to fit my acerbis c35 CF (1" endpipe) but the smallest i can find is 1.35:foul:

So heres the deal, I am going to try several methods of making my silencer temporarily quieter for woods riding and putsin' around. Here's my desired specs

DESIRED SPECS

-removable

-cheap

-cool looking (if visible)

-safe (i dont want to burn my top end)

-no noticeable power change

-around 95 dB

-spark arresting (to please the rangers)

-still sounds good (i dont want it to sound like a blender)

OPTIONS

-silencer end plug

-baffling inner core

-a combination of the baffles and plug

not really much to choose from... but hey, I've got tools, and materials.

the easiest option is to make an end plug... I can spin one in about 20 minutes on the lathe out of good aircraft alluminum, and have it press mount to the inside of my silencer with set screws and an O ring seal... simple enough, and pretty straight forward... my two options within this facet are... a) a QMI style insert..... or a dbDAWG style insert with a baffle bar. which to make is yet to be decided

next is an internal baffle tube, basically a perferated tube with baffles and a spark arrestor welded in, to internally baffle the exaust... a bit more tricky, but maybe a little more effective...

anyone ever tried this? anything easier to do? all help appreciated:thumbsup:

[Santan9]

re-pack it with LOTS of packing

[McgWRATH5150]

re-pack it with LOTS of packing

egghhh.... how much difference does a repack usually make? and even then... it's a seriously track exaust..... goldy locks FMF fatty, and a C.35

[brentn]

The key to restricting sound is surface area and material.

Some materials are excellent at sound suppression, and the more surface area that is exposed to the sound source, the more sound is suppressed.

Baffles would be the best way to make the best silencer for an exhaust, blocking the flow directly and routing it to the sides, but then you restrict flow.

If your going to make a silencer I would suggest a long silencer inner tube with lots of larger packing holes, more area for the sound to the absorbed. Like the others said, lots of packing on top of that.

The easiest way to do this would be to use an existing stock silencer and take out the inner core and drill the holes larger in most places. Also use some really good packing.

The FMF packing that I used on my silencer was crap, it was a fire proof cotton, very light and not very dense, didn't do jack for sound. Does absorb spooge I suppose, although I have yet to see that...

Personally, I would use fiberglass insulation from a house, that stuff is very very dense and fire/burn proof, perfect for a silencer.

If you choose to use it, wear gloves and goggles, glass dust and particles are all over that crap and get into your eyes easily.

Just my two cents.

[McgWRATH5150]

The key to restricting sound is surface area and material.

Some materials are excellent at sound suppression, and the more surface area that is exposed to the sound source, the more sound is suppressed.

Baffles would be the best way to make the best silencer for an exhaust, blocking the flow directly and routing it to the sides, but then you restrict flow.

If your going to make a silencer I would suggest a long silencer inner tube with lots of larger packing holes, more area for the sound to the absorbed. Like the others said, lots of packing on top of that.

The easiest way to do this would be to use an existing stock silencer and take out the inner core and drill the holes larger in most places. Also use some really good packing.

The FMF packing that I used on my silencer was crap, it was a fire proof cotton, very light and not very dense, didn't do jack for sound. Does absorb spooge I suppose, although I have yet to see that...

Personally, I would use fiberglass insulation from a house, that stuff is very very dense and fire/burn proof, perfect for a silencer.

If you choose to use it, wear gloves and goggles, glass dust and particles are all over that crap and get into your eyes easily.

Just my two cents.

thanks for the input... the bigger grate for the core is a good suggestion... unfortunately, I don't have the option of getting a stock silencer to mod, and would honestly just rather outrun the cops than buy a new Q... I will be repacking the C35 anyway, do you think denser is the way to go? thanks

[brentn]

Again more surface area,

So foam for example is awesome at absorbing sound because the little pockets and bubbles provide even more surface area to absorb sound. Sound works in vibrations, so because foam is soft and cushiony it also helps absorb sound.

Foam would be best for sound reduction on the inside in triangular shapes surrounding the core, but you would have to remove the inner core for this to work the best way. Problem is foam isn't fire retardant and it would start on fire

The inner core that holds the packing is the biggest issue IMO, the steel does not help absorb sound at all, so the best you can do is enlarge the holes to give more surface area exposure to the packing material.

I would try fiberglass and see, but the only real way to measure sound reduction would be a battery of tests.

You'd need a sound meter, like ones used for measure home stereo performance.

You'd have to do a test from different distances, using the exact same environment and weather, so all tests done on the same day with the same temp etc.

Do a test 5 feet away directly behind the silencer, and in front. Have the engine ideling for both distances, and then at full throttle for both distances. Then change the distance, go 20 feet behind and in front, repeat.

Record all results, try with a different packing etc.

Alot of work, but could be fun to do to find out what works best for sound suppression, you could try a regular inner core, and a drilled out one to increase the number of variables and the accuracy of the data.

It would give everyone here an idea of what kind of packing would work best, what works worst etc.

Your probably not looking to do all of that, so to answer your original question I would go with as dense and as soft as you can get, that is fire/melt proof.

good luck

[ajd187]

How about just getting a quieter exhaust, and doing your part to help the sport instead of doing your part to ruin it by being too loud?

[pncstod]

How about just getting a quieter exhaust, and doing your part to help the sport instead of doing your part to ruin it by being too loud?

My thoughts exactly!

[brentn]

I'm gona need to bring the bike somewhere to test it then, at full throttle, my bike is loud enought to deafen you.... and loud enough to piss off the neighbors:bonk:

I plan on opening up the holes on the inner core, and repacking it... is there any particular brand of packing that works best?

I can tell you witch one not to get, the two stroke FMF packing is garbage.

How about just getting a quieter exhaust, and doing your part to help the sport instead of doing your part to ruin it by being too loud?

Isn't he? He's trying to make something quieter without spending too much money, there's nothing wrong with that.

[McgWRATH5150]

anyhoo.... I pulled the silencer apart today... this thing has some serious potential. The packing/core was in the worst possible condition, with hardened on spooge completely blocking all the holes.... (that would explain the loudness) but the core is pretty long, with decent sized holes (and a ton of them) the core looks very much like a quiet woods style core. It runs the whole length of the silencer, and then has a 45 degree bend at the end. I made a tool (okay, it's a vice grip with a nail in it) to unclog all the little holes on the core, which works pretty well.... i plan on using a wire brush style paint ball barrel cleaner to really true up the inner core,, then I'll use a wire brush/polisher on the outside, to unspooge, and keep new spooge from sticking as easy... one thing that i noted, was that the packing seemed to be a little bit too tight... as it was not letting the exaust penetrate enough... maybe just a tiny bit looser next time, so it'll last a little longer...

[brentn]

anyhoo.... I pulled the silencer apart today... this thing has some serious potential. The packing/core was in the worst possible condition, with hardened on spooge completely blocking all the holes.... (that would explain the loudness) but the core is pretty long, with decent sized holes (and a ton of them) the core looks very much like a quiet woods style core. It runs the whole length of the silencer, and then has a 45 degree bend at the end. I made a tool (okay, it's a vice grip with a nail in it) to unclog all the little holes on the core, which works pretty well.... i plan on using a wire brush style paint ball barrel cleaner to really true up the inner core,, then I'll use a wire brush/polisher on the outside, to unspooge, and keep new spooge from sticking as easy... one thing that i noted, was that the packing seemed to be a little bit too tight... as it was not letting the exaust penetrate enough... maybe just a tiny bit looser next time, so it'll last a little longer...

try a few larger holes after the repacking and see if it makes a difference

[HNR_Engineer]

A few years ago i needed to silence a V8 Sports Car to pass a DB test for the road. After trying all the suggestions from many experienced exhaust makers the following was the most effective and easiest to fabricate and silence an existing system.

I have never tried this on a motorcycle system but cannot see why the same result would not be achieved.

You need a sheet of perforated sheetmetal with holes similar in diameter to the ones already in the silencer. Cut the sheet to the same length as the current inner perforated tube and then bend up a prism (triangle) from the sheet that will fit down the length of the silencer. So in other words your current perforated tube is round and now you add a triangle inside the round of the same length. If you want to silence it more then you cut the prism in half and weld in a triangle of the perforated sheet in between the two halves like a baffle in the prism and so on.

Easiest way to get the triangle right to fit down the current tube is to draw it on paper so you get your bend lengths right for the sides of the triangle. You can flare the ends if you make it a bit small so that it fits snug.

It was a while ago now that i did this but i remember about 5DB reduction at 4500rpm on the V8.

There was no notable reduction in power.