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slowmoto

Making a 2-stroke extra quiet

21 posts in this topic

I've been riding mainly trials bikes and quiet 4-strokes (XL250) for the past 30 years and this year got my first MX bike (KX100). Stock, it is so loud at high rpms it gave me a headache. I added a dbSnorkel and wrapped the pipe with silicone and rubber and it has made a huge difference. 1st layer is made from a silicone baking sheet, then another layer, then a layer made from a truck inner tube. Used silicone tape to finish the ends. It made the pipe weigh twice as much. Much of the annoying high pitch was coming from the stock expansion pipe. At low rpms it is whisper quiet. I can now actually hear the piston, crank and gears working.

exhaust.jpg

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Why not get something like a crf150r? You just got rid of one of the fun parts of a 2 stroke. The ping ping pinging.

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I've been riding mainly trials bikes and quiet 4-strokes (XL250) for the past 30 years and this year got my first MX bike (KX100). Stock, it is so loud at high rpms it gave me a headache. I added a dbSnorkel and wrapped the pipe with silicone and rubber and it has made a huge difference. 1st layer is made from a silicone baking sheet, then another layer, then a layer made from a truck inner tube. Used silicone tape to finish the ends. It made the pipe weigh twice as much. Much of the annoying high pitch was coming from the stock expansion pipe. At low rpms it is whisper quiet. I can now actually hear the piston, crank and gears working.

exhaust.jpg

You win. That is the quietest setup I have ever seen. I can't imagine it being any quieter than what you have . You can probably go underwater a littlelonger at river crossings too with the snorkel. How is the smell of the rubber after you have been running the bike for awhile? Isn't it kind of strong?

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Bingo! This is very similar to what I've been trying to do. I've been looking for some sort of silicone sheet that I can wrap around the expansion chamber, like a candy cane, with a stripe of exposed pipe showing for heat dispersion.

Can point me to an internet source for silicone sheet and tape?

Edit: My 2010 300XC-W has a pretty quiet stock exhaust that I've added a DbSnorkel to. With some expansion chamber muffling it's gonna be sweet.

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Very interesting setup! A KX 100 is probably one of the louder smokers out there, so you have done a good job. I've also got a db snorkel (on a 250), and I've wondered if you could reduce the pipe sounds by reducing resonance. Maybe the pipe would not need a full wrap, but just a spiral strip to reduce the "ringing" of the metal.

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I'd also be interested in more information about the silicone baking sheet.

I'm in the middle of a similar expansion pipe wrap. I'm going to try using fiberglass muffler packing (the kind of 4 storkes that's woven into sort of a blanket) for temperature tolerance and sound absorbtion. Then I may do an outside layer of fiberglass cloth / resin to make a waterproof outer shell.

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i really want to know how the silicone is holding up to the heat as well.

please update us.

maybe a soundclip or youtube video of it running?

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Nice job! These are exactly the kind of solutions we need to keep riding areas open. It does have a unibomber look to it though....

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Why not get something like a crf150r? You just got rid of one of the fun parts of a 2 stroke. The ping ping pinging.

A crf150 is louder than a 250 2 stroke....

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I got the silicone baking sheet from Target. They have the burgandy ones in the store and black ones online. Search for silicone solutions baking sheet. I joined the strips together with small pieces of the sheet glued on both sides with automotive silicone adhesive, which is also a good way to patch holes on the dbSnorkel. I actually think that the truck innertube will work by itself. It gives a vulcanized rubber patch smell for about 4 hours, then goes away. 2-stroke exhaust doesn't get very hot so rubber might be good enough. The cylinder head O rings are made of rubber. Automotive exhaust wrap doesn't absorb sound as good as silicone and rubber. I tried it and it won't wrap around an expansion pipe because it doesn't stretch. It would be a good option for 4-strokes.

The silicone is vulnerable to tearing and the rubber is much tougher. The silicone has held up for years on my trials bike and it looks like the rubber innertube will last even longer. A car heater hose is covering the small diameter of the which doesn't seem the make that much difference. If you bang on a stock expansion pipe, it is like a giant cowbell, so that is where much of the noise is coming from. I now also have an exhaust guard wrapped under the rubber. The finishing tape I use is called Xtreme Tape Silicone Stretch Wrap 1" X 10' Black which is available at Amazon, Fry's electronics store and your local hardware store under different brand names.

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hi

i have been trying to call db snorkel from canada.....800 number does not work....do you have a local number for them? I have a 1979 husky that does not pass noise tests....

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It's a small company so they're not always by the phone. Better to use email. What's to ask? All the info is on the site.

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we tried to send note to them.......having trouble with their registration page.....which is why I am trying to call them.....do you have a direct email address as can't find that either on their website....

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we tried to send note to them.......having trouble with their registration page.....which is why I am trying to call them.....do you have a direct email address as can't find that either on their website....

I just called 1-800-694-0287 and got the owner. He said you can email dbsnorkel@sbcglobal.net

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Nice job! I used header wrap for a pipe a while ago and made a Flow-Master style silencer with chambers. Made a huge difference. You can install a pipe guard too.

Pipe006.jpg

Silencer004.jpg

Silencer009.jpg

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nice work!

that expansion pipe rings like a bell; I was planning on putting a header wrap on it to keep the contact temp down, then using some "tek-lite" car audio noise reduction material on top of the wrap.

the only things I'd add are:

-the airbox also makes a good amount of noise. don't believe me? take off the seat, and gently stroke the throttle...louder, eh? for that reason, "seal off" the rear corners of the airbox, so sound can't slip through the corners,

-to further dampen that intake roar, lay some sound damping materials on the inside of the side panels and under the seat

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