Ultra quiet 70 CC?

[JosephGarcia]

you could pinch it in the opposite direction to push out the previous pinch, and find tune the circle by hammering. crude but it works, i did this to some bicycle frames and forks before.

 

[kevbo]

IF you run an expansion chamber, then the smaller the exit (stinger) the MORE power you get....the extra backpressure results in extra "supercharging" effect from the tuned pipe. The engine will also run hotter, so there is a limit to how far this can be pushed. My point is that quiet operation often goes hand in hand with increased backpressure, and with a tuned pipe, you needn't trade performance to get it.

That said, a good deal of the noise from any aircooled engine is not coming from the exhaust. It is comming from the cooling fins, sounding boar....er I mean clutch cover, and so forth. This tends to be higher frequency stuff, and fairly obnoxious....a good deal of the "ring" in the "ringdingdingding" sound dirt bikes are known for.

Stuffing some polymer blocks between the cooling fins to damp vibration is one of the tricks used to help quiet air cooled engines.

 

[joelvanderhoof]

Ok I think I've found some middle ground. I wrapped the pipe about 1/2 way with the packing and that helped quiet things down a bit without killing the power.

 

[joelvanderhoof]

I'm also thinking that a combination of a boost bottle and some silencer packing will really help things

 

[Dockspa1]

Hey Joe, That pinch in your pipe looked like it was there on purpose. What size was your motor? maybe this is where they do their cheap Happy Time back pressure tuning. Thay can use the same pipe and just crimp it in different places for different cc motors.
Just a thought!
Doc

 

[Alaskavan]

I think Doc might have something there. I don't know squat about exhausts. But it looks to me like it's made to be that way. Perhaps it forces some of the exhaust to go out the holes on one end of the pipe into the chamber, then allows the exhaust to go back in the holes in the other end of the pipe before exiting. Whatever. If you've found something that quiets it down and works, that's good.

 

[Herrmanator8]

i built a really nice air filter that doesnt allow sound to emit from it and it keeps fuel out of the filter and in the carb. although a separate exhaust might muffle it a little more that the normal exhaust, it still wont be that much quiet...actually, when im cruising top speed my gearbox is louder than the engine itself.....

jon

 

[JemmaUK]

Hey Joe, That pinch in your pipe looked like it was there on purpose. What size was your motor? maybe this is where they do their cheap Happy Time back pressure tuning. Thay can use the same pipe and just crimp it in different places for different cc motors.
Just a thought!
Doc

Im not an expert on exhausts either but personally that looks designed in for a purpose. What I think happens is that the engine-side flow is squirted out of one set of holes to swirl in the body of the silencer. The pressure then pushes the fumes out via the holes after the crimp. Take the crimp out and you would effectively have a straight through - which is not good for quietness. Reducing the amount of packing and the fineness of it would probably help the torque problems - from the pictures whatever you have used seems very finely woven which needs more pressure than a coarser material.

The way I have done my silencer is keep the primary part as a pure resonator with a single baffle in the middle made with the bottom of one can and the top of the other. These are angled to be 180 to each other. The flare is packed with foam wadding from a tool kit I have. It seems to silence the engine brilliantly and so far has cost me 3 440ml beer cans, sellotape and 3 heavy duty cable ties (and a few hours fettling testing and re-fettling).

good luck with the silent running

Jemma xx

 

[gauge]

hey hermonator u should see my air box and air filter its not restrictive and it filters alsome i dont get any dirt past my filter now and it is to clean

 

[Dockspa1]

Jemma have you got some pics of the invention you were talking about.
Interested.
Doc