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Discussion Starter · #1 · (Edited)
Hello friends,

I am a new rider from Portugal who recently purchased a CBR 250 2011 MC41 as my first bike for commuting to work and college, and I got a decently good deal as it is in good shape with around 22k kilometers, but the only downside is that it has an (fake, I guess) akrapovic slip on that is loud as hell. It came with a db killer like this one but it is not enough (I've had issues with my ears in the past, so they're a bit sensitive to loud noises), so I was thinking about purchasing an additional db killer like this one that goes in the other side of the slip on, but I am wondering if that could damage the engine somehow.

I already ride using earplugs, but I still would like to get it as quiet as possible.

How likely would it be to be problematic to use both of those together?

Thank you.
 

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Personally, I think you're just throwing good money after bad trying to "rehabilitate" a cheap, knock-off slip-on muffler. Slip-ons are designed to do just that, with no adjustments to fuel mapping. If adding that second silencer changes the designed specs of the pipe you could end up with poor performance and possible engine damage.
I think you'd be much better off replacing your "fake" Akrapovic with a new, quieter slip-on exhaust. Companies like Delkevic still make reasonably-priced, good quality slip-on mufflers at a fraction of what a new Yoshimura or Akrapovic would cost, including longer stainless steel or carbon fiber mufflers with dB inserts that can be as quiet as a stock pipe.
"MacGyvering" an aftermarket slip-on for any reason is probably not a good idea, IMO.
 

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What about trying to locate a stock system? That would be the best solution IMO.

If you did go with the additional restrictor, it may lose some power over stock, but I don't think it would cause any damage.

I'm not sure how effective adding that would be, and it may be a challenge.
 

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Hello friends,

I am a new rider from Portugal who recently purchased a CBR 250 2011 MC41 as my first bike for commuting to work and college, and I got a decently good deal as it is in good shape with around 22k kilometers, but the only downside is that it has an (fake, I guess) akrapovic slip on that is loud as hell. It came with a db killer like this one but it is not enough (I've had issues with my ears in the past, so they're a bit sensitive to loud noises), so I was thinking about purchasing an additional db killer like this one that goes in the other side of the slip on, but I am wondering if that could damage the engine somehow.

I already ride using earplugs, but I still would like to get it as quiet as possible.

How likely would it be to be problematic to use both of those together?

Thank you.
I didn't know there was an option to add a decibel killer from the back side as well. Sounds like an excellent idea, and not problematic at all, except for the price. 20 euros, in my opinion, is too much money to invest in your case. Maybe I would buy one from AliExpress(For 8.8USD)? If you have sensitivity, and this is also recommended because of the wind noise, using earplugs is always good idea.

Are these sizes suitable for you?:
Microphone Font Material property Screenshot Cylinder
 

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Discussion Starter · #5 · (Edited)
What about trying to locate a stock system? That would be the best solution IMO.
I'll definitely give it a go, I admit that getting the stock system would be the ideal scenario for me. Thank you for your input.

I'll likely try the restrictor I linked and see if I find any issues with power, or if it does anything for reducing the noise.

Maybe I would buy one from AliExpress(For 8.8USD)?
I will take a look at it, but from the image it seems that the size could fit just fine. Hopefully I can get it delivered in a few days, but I'm absolutely wearing ear plugs in the meanwhile.

Thank you!
 

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I'm pretty sure it'll be fine because the 250r isn't really throwing out all that much exhaust. They put these slip-ons on 600cc bikes and bigger. The header pipe is your biggest restriction. If the sound is truly an issue, your only solution would be to pack the muffler with an appropriate steel wool or fiberglass insulation. dB killers really don't live up to their name and testing at just 2 or 3 dB loss.

As a side note, I'd wager if you counted up the holes and multiplied by the size of each hole, the area would be 3 or 4 times that of the header pipe.
 

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Designs of aftermarket slip-ons compared to factory muffler are completely different. If you want quiet, best to get factory muffler with multi-chamber design. There must be millions of them laying in back of people's garages. Seems 1st upgrade most people do is some loud aftermarket exhaust.

Put up wanted-ad here and on local websites like craigslist. I'm sure you'll get hundreds of responses.
 

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.... your only solution would be to pack the muffler with an appropriate steel wool or fiberglass insulation.
In the original CBR250R?(2011-2013) mufller , which is considered Very Quiet,
there is none of the materials you mentioned (wool or fiberglass insulation).
But yes there are 4 chambers to reduce noise, and it works great:
Rectangle Slope Handwriting Font Parallel
Bumper Material property Wood Automotive exterior Automotive lighting

.... dB killers really don't live up to their name and testing at just 2 or 3 dB loss.
A decibel is a logarithmic unit of measure.
The difference of 1db measurement units is 10 times,
the difference of 2db measurement units is 100 times,
and the difference of 3db is 1000 times.
Therefore, db killers are the appropriate name for toys that provide such a difference(2-3db).
 
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In the original CBR250R?(2011-2013) mufller , which is considered Very Quiet,
there is none of the materials you mentioned (wool or fiberglass insulation).
But yes there are 4 chambers to reduce noise, and it works great:
View attachment 45574 View attachment 45573
Chambers are better. I do believe a vehicle should remain stock as much as possible (excluding of course engineering mistakes). I think joaomatos0 is trying to use his aftermarket muffler and is looking for ways to quiet what he already has. From what I read, he didn't get the Honda muffler when he bought the bike. I suspect he is looking for the least expensive way to reduce sound.
 

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Chambers are better
YES AND As far as I understand, the other materials you mentioned are mainly intended to insulate heat.
... I suspect he is looking for the least expensive way to reduce sound.
YES for that I already wrote the following response earlier:
I didn't know there was an option to add a decibel killer from the back side as well. Sounds like an excellent idea
I really like a quiet exhaust. I have the original quiet exhaust, and maybe I myself will consider purchasing a rear db killers muffler too, so that it will be even quieter(y):coffee: (the attached photo)?
I need to check that the measurements are appropriate.
Microphone Font Material property Automotive tire Screenshot
 

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I need to check that the measurements are appropriate.
I measured. The Inner Diameter of the pipe is 34.9mm (O.D 38mm). And then inside the muffler the diameter expands (the area of the catalytic converter). So even if I find some short db-Killer to put in the pipe, there is nothing to hold it, the pressure will push it to the catalytic converter (which for me is an empty space). So I give up on the idea of quieter than quiet.
 
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