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Discussion Starter #1
Hello

I'm looking for muffler from aliexpress because I don't want to spend hundreds of euros to a muffler. So there are really good ones for like 75-90€ but the problem is that the exhaust inlet port is 51mm the one where the exhaust pipe is connected.

My exhaust pipe is 32mm diameter. First of all it might look pretty weird to have 51mm muffler but the question here is that how will this change the performance? So will there be too little backpressure as it's bigger than my pipe? Should I just buy 38mm one or 51mm one?. My stock muffler sure is limiting the bike but driving without it seems like theres no power anymore.

So I don't want to lose power for better sound and better exhaust flow, will this happen? I'd like to get a 51mm one because they look real rather than the 38mm ones look like they are made of plastic.

Bike is Derbi 125 Baja with 149cc bore.
 

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If something has changed with the power output recently, the muffler is not likely the cause. You won't get much of a boost in power, if any, by changing exhaust on a 125 cc engine. Some change in sound can be obtained, for sure.
 

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Discussion Starter #3
If something has changed with the power output recently, the muffler is not likely the cause. You won't get much of a boost in power, if any, by changing exhaust on a 125 cc engine. Some change in sound can be obtained, for sure.
Nothing has changed but I'm just a bit worried if too big muffler would affect the performance in negative way. I'm going to change main jet to bigger and change air filter to free flowing one. I want better sound and the current muffler weights about 5kg and after a long ride it's so hot you could cook on it.
 

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Simple answer is, yes, changing the muffler will affect performance. Generally, louder, larger, free-flowing mufflers reduce low rpm torque, while increasing high rpm horsepower. This is why good muffler systems cost; they are engineered to change performance in a controlled way, rather than just welding some tubes together.
 
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