loud silencers 750 SF

Bert Reganze said:
It is completely filled with packing wool; no gram can be added anymore.
Click to expand...

Wool's pretty ineffective at the best of times - as you have discovered  :D.  Essentially, to reduce noise, you have to make the gas loose energy - which is done by making it travel further/work harder/slow down.

That's the concept behind the SF1-3 colostomy bag arrangement.  And that works.  Wool?  Nah ...
 
The (interesting) drawing shows the same principle as car mufflers. It's function has been described very well by Lothar. So it's important to work out which type you have. I actually find the packing makes quite a bit of difference on the ones I've made, but they use heavily perforated sheet.

Straight thru Contis (after removing 'cornering limiter the junction' box under the motor) are loud but not offensive and pass roadworthy here in Australia. Too loud for a Ducati Club track day at Phillip Island though!! Ludicrous noise limits.
 
And don't try similar tubes made of alloy just because of the weight - you will lose them sooner than you think...  ???

(guess how I know... ) :-X

;)

years ago, when I had a 3-1 megaphone exhaust on the Jota and I got sick of all the stones thrown on me when I passed people, my brother developed a very cool insert: one of these mesh-type tubes (unfortunately made out of to mild aluminium...) stuck into the exhaust. In the center of that tube, he made up 2 half-circle plates with an axle so they worked like a flab. Both were pulled towards the entry side of the "muffler" by springs, each with differend load. Theory - and at the end really working well - was, that up to maybe 2.000 revs, both flabs are closed. then one opens and - maybe at around 4.000) the second one.

It worked really well and harmonized the noise to a good, full bark still, but more acceptable. Unfortunately, the whole thing was held in place only by 2 screws and on a highway run, the screws cut through the alloy like a hot knife through butter. The guy behind me almost was hit by the parts spit out of the exhaust...  ???

We never replaced it, but I would if I ever would ride a 3-1 megaphone again. But then with a steel insert like shown by Thomas link (and with more parts holding it in place... )
 
Early Lenhardt & Wagner exhausts for the old aircooled  Jap bikes had a removable insert that slid into the end opening of the exhaust. Careful observers identified the insert as the tail piece of a VW Beetle :D

Gerald
 
Lothar, sounds like your brother constructed a homemeade Exup valve. It worked for Yamaha, why not a triple Lav! All about backpressure and torque curves.
 
A perforated tube as in the link Thomas has put up, tightly wrapped in fibreglass, is what keeps virtually all the classic bikes racing here within the strict track noise limits - much stricter than on the road. The smaller the volume of the canister the harder to get it quiet, and the larger the perforated tube and the bigger the holes, the harder to get it quiet. The holes in the tubes in the link seem pretty big to me, much more smaller holes would be more effective, also in keeping the fibreglass packing from needing replacing so often, but a road going old Laverda twin is not going to be at full throttle much at all so it wouldn't be such a problem, and such a low power motor wouldn't need a very large diameter tube either. I don't think it would be difficult at all to shut it up with that system, and with a chromed flat end piece at the outlet that looked like the original it wouldn't offend the riviteers.
 
Thomas aus LAU said:
Could you please open the little screw at the end and pull out the inner part of the silencer.
Whith a photo we will see what we can do.

Do you have the connection between the two hoses near the cylinderhat?

30-40 years ago i had several times the job to reduce noise good sound when i had to go to the technical check (T?V) of my bikes.
It is possible to reduce the noise, but you will get an different sound.

Best Thomas aus LAU
Click to expand...

Hi Thomas, here are the pictures of the inside
 

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Bert Reganze said:
Hi Thomas, here are the pictures of the inside
Click to expand...

It looks as if there is also foil wrapped around.

At most, this can be used outside as a closure for easier insertion.
Otherwise the wool must be "open" so that the sound pressure can penetrate through the holes in the wool so that sound energy is destroyed there.
The wool must also not be wrapped/pressed too tightly.

Best Thomas aus LAU

 
Laverdalothar said:
Hi Bert,

it is fairly easy if you are able to weld. A DB-eater is basically nothing else but an reflection type damper. Done right, it reduces noice without sacrifying power or torque.

Measure the inner tube diamter of the back-end of the muffler and  see if you can find one that fits. they come in differen diameters and are screwed in just like the damper-insert that you have already (but in this case, in addition to the damper insert!). See f.e.:

36mm:
https://www.amazon.de/dB-Killer-Universal-dB-Eater-Kr%C3%BCmmer-Auspuff/dp/B078K2TRXL/ref=asc_df_B078K2TRXL/?tag=googshopde-21&linkCode=df0&hvadid=345518677632&hvpos=&hvnetw=g&hvrand=16428713744983719567&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9044751&hvtargid=pla-751378586310&psc=1&th=1&psc=1&tag=&ref=&adgrpid=75266748688&hvpone=&hvptwo=&hvadid=345518677632&hvpos=&hvnetw=g&hvrand=16428713744983719567&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9044751&hvtargid=pla-751378586310


or

35mm:
https://www.amazon.de/MASO-Motorrad-Auspuff-Schalld%C3%A4mpfer-einf%C3%BCgen-k%C3%B6nnen/dp/B07QFPHQHB/ref=sr_1_8?__mk_de_DE=%C3%85M%C3%85%C5%BD%C3%95%C3%91&dchild=1&keywords=db+eater&qid=1595848531&s=automotive&sr=1-8

with the last one, you can see how they are build. If you can weld and drill the holes, you can produce one to fit your exhaust quite easily... ;)
Click to expand...

Hi Lothar, that sounds like a good option. Can I place these db killers at each position in the perforated tube? What is more effective, at the end, middle or at the beginning of the silencer? kind regards Bert
 
Thomas aus LAU said:
It looks as if there is also foil wrapped around.

At most, this can be used outside as a closure for easier insertion.
Otherwise the wool must be "open" so that the sound pressure can penetrate through the holes in the wool so that sound energy is destroyed there.
The wool must also not be wrapped/pressed too tightly.

Best Thomas aus LAU
Click to expand...

yes, this is a layer of paper and paper-tape for easier insertion, only at the outside. I tried to put as much as possible wool, I understood from other sites that this would be the best. You mentioned that you had some solution to reduce the noise. Is that applicable for this type of damper?
 
Thomas aus LAU said:
When i got my first Laverda build 1972, it was relativ new. There was no wool inside the pipes.

In opposite to the SFC-pipes (see picture) the open "room" in the middle is missing and the drilled hose inside goes from the end till the first "wall/schott".
I will take the long endoscope-camera and will have a look inside.

IMG_6510.jpg


Best Thomas aus LAU
Click to expand...

If I understand well, this picture is for SFC pipes, without wool, and probably quite silent?
 
Bert Reganze said:
Hi Lothar, that sounds like a good option. Can I place these db killers at each position in the perforated tube? What is more effective, at the end, middle or at the beginning of the silencer? kind regards Bert
Click to expand...

They are typically installed at the end. You have a screw already there which might be usable to also install the dB-eater.

But first pull the insert and see which type of damper you have. if it is a reflection type damper (like the one in the Thomas's pic), go the dB-eater route. If it is an absorbtion type damper (tube goes all the way through to the header/downpipe; you basically can look into the damper and see full light with no restrictions at the other end), than putting in damping material would be my first (more easier) choice
 
Bert Reganze said:
If I understand well, this picture is for SFC pipes, without wool, and probably quite silent?
Click to expand...

I don't think so... The first Laverda with a relatively calm exhaust note was the RGS. Even more so, the Zane models (if no Termignoni were installed). Everything else was loud. the 750's more than the Triples (with standard factory exhausts).

But compared to the 2-1 Megaphone, you are propably right, then they are quite silent...  ;)
 
As I'm in the process of building an exhaust system that I want to be quieter than a 2/1 mega(!!!) I'm interested in the thread. I'm using a straight thru absorption type muffling system. As you can see from the pics, my perf tube has a lot more holes and they are a lot smaller than yours - perf tube comes with a % figure for 'open' area. I'm also using a fairly large (93mm) canister plus stuffing baffle wool into the mega part so hopefully it will kill a few Db's - it's not a motor in a state of tune that will work with excessive internal (or any) baffling plates or small diameters.

I've also bought some stainless 'fywire' to wrap around the perf before the baffle material goes on.

You may find you can quieten yours with a different type of perf tube - not that hard to modify as it's basically just a parallel cylinder..

 

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Laverdalothar said:
They are typically installed at the end. You have a screw already there which might be usable to also install the dB-eater.

But first pull the insert and see which type of damper you have. if it is a reflection type damper (like the one in the Thomas's pic), go the dB-eater route. If it is an absorbtion type damper (tube goes all the way through to the header/downpipe; you basically can look into the damper and see full light with no restrictions at the other end), than putting in damping material would be my first (more easier) choice
Click to expand...

Hi Lothar, it is an absorption type damper which is already filled with pretty much wool (see pics posted earlier). Still it is very loud. I just ordered a set of db killers as suggested.
 
ah - oversaw the pics, sorry. As Thomas (I think) said, the wool must be able to take some of the emissions, else you have nothing else but a straight through exhaust. as it looks, this is not proper Material but just glaswool from roof insulations...

look at the following video, maybe you need to change the material...:

https://www.youtube.com/watch?v=RNxKO18I-3I

 
Thomas aus LAU said:
Could you please open the little screw at the end and pull out the inner part of the silencer.
Whith a photo we will see what we can do.

Do you have the connection between the two hoses near the cylinderhat?

30-40 years ago i had several times the job to reduce noise good sound when i had to go to the technical check (T?V) of my bikes.
It is possible to reduce the noise, but you will get an different sound.

Best Thomas aus LAU
Click to expand...

Hi Thomas, you mentioned that it is possible to reduce the noise. Is this possible for my type of silencer. Could you give me advice how you managed to do this for the tuv check? kind regards Bert
 
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