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Old 07-04-2015, 05:11 AM   #1 (permalink)
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I weighed my exhaust 5.5kg + exhaust building

Hello,

I weighed the exhaust on my cbr125r and it weighs 5.5kg. I wonder if I could build sub 1kg underslung exhaust that works, is not too loud and costs less than $30.

I am considering the following.



Inner tube (weight <380 grams)

1" diameter, 0.9mm wall thickness, 70cm long mild steel tube. Last 35cm will be perforated.

Exterior muffler tube/expansion chamber (weight ?)

3" steel end cap at either end. 35cm of Light weight sheet metal (maybe aluminum) riveted to end caps. End caps secured with tube clamp at engine end and bolted at the exit end. And gaps sealed with some sort of sealant.

Insulation (weight ?)

I have not researched exhaust matting but I will look for something that will not get sucked through the perforated inner tube. Some what loosely packed to allow some expansion.

Baffles

I will see how loud the straight through exhaust is and add baffles as needed. I don't want an obnoxiously loud or illegal exhaust.

MPG

It is unlikely there will be any difference in MPG but if I am successful in building a functioning exhaust I'll see how it goes for a few tanks of gas and determine if there is any noticeable change. As long as it does not decrease my MPG it will be worth it because the stock exhaust is both aerodynamically and aesthetically jarring.

Conclusion

If anyone has tried building an exhaust system for a four stoke motorcycle and can offer some advice please share it so you may save me some grief and ensure the success of this DIY project

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Old 07-04-2015, 06:30 AM   #2 (permalink)
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My son had a CB125E with an exhaust of similar weight.

He chopped it just after it straightened out under the engine and fitted an aftermarket slash cut / turn out muffler that finished just behind his heel.
It was too loud on it's own, so he added an extra baffle inside the muffler.

This was part of a weight saving exercise that included removing the centre stand, the passenger foot pegs and brackets, as well as other small items.

With the muffler and pipe finished in black, it was almost invisible when on the move.
He's since sold that bike, so I can't post any photos, but I think the muffler and baffle were just ebay items.
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Old 07-04-2015, 07:30 PM   #3 (permalink)
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Getting an exhaust pipe with less than 1kg doesn't seem so easy at all, but it also doesn't seem impossible. For soundproofing and some modest degree of thermal insulation you can use the same glass wool used to insulate refrigerators and ovens.
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Old 07-05-2015, 03:38 AM   #4 (permalink)
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Quote:
Originally Posted by D.O.G. View Post
My son had a CB125E with an exhaust of similar weight....
Before deciding on the previously mentioned muffler, we trialed an old 250cc chinese trail bike muffler that we had kicking around.
It was a bit smaller than your design, but still larger than the item he ended up using.
It featured an extruded alloy chamber and cast alloy end plates. The internal steel baffle added a bit of weight, but it would have still been close to your target weight.
I liked it, it had a really nice sound, but it wasn't my decision.

It might be worth your while checking out what's available at a bike wreckers near you.

In regards to non-standard mufflers and the law, it'll be a lot easier if you can get something already ADR approved.
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Old 07-05-2015, 06:29 AM   #5 (permalink)
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Why would you build a muffler when you can buy one for so little? Get a Vibrant aluminum muffler, I think they weigh like 1 pound.
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Old 07-09-2015, 10:08 AM   #6 (permalink)
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Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
Getting an exhaust pipe with less than 1kg doesn't seem so easy at all, but it also doesn't seem impossible. For soundproofing and some modest degree of thermal insulation you can use the same glass wool used to insulate refrigerators and ovens.
Rock wool has even better sound insulating abilities from my experience, might be bit heavier, but difference is perhaps not too much.

For me low level of sound is one aspect of low environmental impact of transportation, so I have modified my scooter exhaust to be a lot more quieter than original and also it seem to flow better than original, weight is bit more though, but better flow reduced fuel consumption more than weight increase increased so in total fuel consumption was reduced while power was increased.

Cost was next to nothing, little bit of electricity, rock wool I had around because of house renovation, little bit of time.

I used metal wire net to be 'pipe' for exhaust inside the silencer, then around that I packed rock wool, because I wanted maximum silencing I did pack it loosely, I could of packed it tight when it would of been better flowing, also using less holes would improved flow even more, but that was not my primary goal.

Old exhaust pipe was big empty can and at the end of it there was tiny silencer, I filled silencer and big empty can with rock wool, had to of course cut that big can open.

In 2-stroke that would of not been possible, because exhaust is important to be just right, but for 4-stroke exhaust is not so important as long as there is not too much of resistance.

Similar level of sound reduction would cost over 80 for good quality silent silencer, so I think it was worth it.
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Old 07-09-2015, 02:46 PM   #7 (permalink)
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Quote:
Originally Posted by jtbo View Post
Rock wool has even better sound insulating abilities from my experience, might be bit heavier, but difference is perhaps not too much.
I mentioned glass wool because its availability is easier back here.
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Old 07-10-2015, 08:58 AM   #8 (permalink)
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Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
I mentioned glass wool because its availability is easier back here.
Oh yes, there are probably quite bit of variation depending where one lives.

I know in US there is rock wool in hardware stores and here it is one of the most available insulation materials, but I have no idea how things are at southern hemisphere.

Even here in Europe there is big differences in availability of some construction materials and how buildings are constructed.

More variety, more options I guess

But be careful with glass wool, it has very tiny fibers and even installing it to muffler is not large amount, it might be good idea to wear a respirator and gloves, darn stuff is bit dangerous.
Good practice with rock wool also.

Glass wool is kind of tiny shreds of glass, it dusts a bit and those tiny bits of glass you can't even properly see can end up into lungs. It has small cancer making risk which is still under debate, so it is advised that anyone handling the stuff uses respirator.

It is more of concern when doing many houses, but how these things work it might be good idea to minimize risk, I mean some people are said to win even in a lottery.

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