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Opinion on db`killer in header

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For the experts

DSC00190.jpg

Bike crf250

To meet the new regulations over here i am about to built a header with this "bomb" looking silencer (see picture)

My theory is that this will flow better than same muffler with an db.insert or cone , this will hopefully allow me to run a more open muffler

this is an experiment as the stock system actually is a bit to loud for our 2010 regulations and something has to be done

The header will be built similar to stock just with this in position like the powerbomb

What are your opinion ,will it ruin the flow/backflow in the header, how much will it affect on soundlevel, etc etc any thoughts is welcome

Thanks

Kim

Edited by 450DK
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It will change the "tuning" of the head pipe more so than a powerbomb.

It might be easier to use a FMF quiet core.

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OK i was afraid so, i will have to try it on a dyno

but after using a lot of money on mods for the engine i think its sad to have to put on a restrictive muffler.

but ofcourse in the end it can be the only solution if this system will make even less power

i will test it with the stocker and one with 1,5"core strait, i am also curious to see how the sound level will be

Thanks

Kim

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Looks kind of like a pre-silencer for a car, done just after the headers but before the mufflers for further noise reduction.

This is a straight through design?

I think it would work, but it's already mentioned that it may change your tuning. Flop it on the dyno and see,

Do you have a DB meter?

If you don't they sell ones for home stereo that allow you to properly tune speakers for the right volume. Would work perfectly for a bike.

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Give it a try , you learn from trying and seeing what works.

exactly , but i kind of hoped that someone had tryed something similar

Yes it is strait through

I have a DB meter and it was just over the limit, our organization has also tested the crf and said it was to loud, i think they will reject many bikes this year exept for the KTM they have seen it coming

Kim

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Send me one , I will run it on my dyno.

I might hold you up on that one:thumbsup:, i will finish it and dyno it here local to see how it affects the powercurve and AF, and if it does well i will see if i can find the time to do another one

i have made some other variations of the concept but it all happens in my limited sparetime

I will post when there is progress

Kim

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So here is the 1st one ,on the bike

02042010.jpg

02042010_002.jpg

I will take it to the track tommorow

and also measure if it has reduced the db level

Maybe next week it will be on the dyno

Kim

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Is there any fiberglass packing between the perforated inner tube and the outer shell? That seems to be just a small resonator muffler design, which are much quieter when filled with packing (and, conversely, get very loud when the packing gets blown out).

I wonder if you'd get the same noise reduction by adding that mini resonator to the output of the existing muffler.

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Is there any fiberglass packing between the perforated inner tube and the outer shell? That seems to be just a small resonator muffler design, which are much quieter when filled with packing (and, conversely, get very loud when the packing gets blown out).

I wonder if you'd get the same noise reduction by adding that mini resonator to the output of the existing muffler.

I didnt put any packing material in it

I ended up dropping the projekt as there was almost none noise reduction , and still couldnt meet the regulations

I currently run the fmf Q4 with stock header and it does very well

Maybe ill get back to it when it comes to wintertime again

Kim

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The concept has merit. It's basically adding a supplemental small glasspack muffler. That design of straight through resonator muffler creates little restriction.

But to see appreciable reduction in noise, it might have to be significantly larger in volume and to be filled with fiberglass packing.

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I didn't put any packing material in it

I ended up dropping the project as there was almost none noise reduction , and still couldn't meet the regulations

I currently run the FM Q with stock header and it does very well

Maybe ill get back to it when it comes to wintertime again

Kim

My concern would be your baffle as designed would create a lot of turbulence in the header and reduce flow, especially being unpacked. But even if packed, in such a high velocity area in the exhaust turbulence could still be a problem.

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The FMF Power/Mega Bombs are made along these lines; a perforated core with no packing. The main difference is that the perforations are much larger and much fewer (some of the perforations are slots), and the intent is for the segment to both dampen and resonate the pressure waves within the header for tuning purposes. It was never intended as a sound killer, and there isn't much evidence that it serves as one.

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My theory from the beginning was that , just a small noise reduction in the header would add up the effect when passing the muffler (it didnt:lol:)

I prepared several different designs to test , but guess what,

there is just not time enough

Kim

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FMF claims up to a 1.5db sound reduction with the megabomb. To my ear every time I have tested one the bike seemed a bit quieter. I have a db meter and at some point I will test it.

As far as holes in the megabomb header I have never seen more than 2-4 around 6-7mm in diameter.

I think the concept does reduce sound other wise Pro Circuit wouldn't bother with them on their pro bikes.

Kim, I would toss the baffle and just stagger 2 larger holes and increase the volume of your outer chamber. In my RMZ mega there are 2 holes opposite of each other. In the Honda there is only one hole.

Edited by 455

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FMF claims up to a 1.5db sound reduction with the megabomb. To my ear every time I have tested one the bike seemed a bit quieter. I have a db meter and at some point I will test it.

As far as holes in the megabomb header I have never seen more than 2-4 around 6-7mm in diameter.

I think the concept does reduce sound other wise Pro Circuit wouldn't bother with them on their pro bikes.

Kim, I would toss the baffle and just stagger 2 larger holes and increase the volume of your outer chamber. In my RMZ mega there are 2 holes opposite of each other. In the Honda there is only one hole.

Allways nice with some "insider" info

it was never my idea to copy their design, but i did see that they claimed a 1.5db reduction

i also have my own db-meter and tested several times ,and if there was a reduction it was not big enough

Kim

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