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