Home made silencers.

[Bob Purton]

I'm thinking about making my own silencer for a villiers 9e 2 stroke, has anyone on the forum done this before who can advise me? I seam to remember years ago dismantling a Bond minicar one, the earlier ones came apart and as I recall there wasn't much to it! I think it was just a center tube with lots of holes in it that was the baffle with two end caps, the gap between the center baffle and the outer casing being stuffed with fiberglass wadding. I'm, looking to make a fairly compact silencer, maybe 12 to 14 inches long and about 3.5 inches in diameter. Any observations or advice please?

[Jim Janecek]

1: you can use steel wool inside instead of fiberglas stuffed into a straight tube.
2: doesn't the silencer for a 2-stroke have to be "tuned" (sort of) for the engine?  It does more than simply muffle the sound.

[Bob Purton]

Thanks Jim, I read somewhere that you can get stainless steel wool which sounds even better. About the "tuning", thats why I thought if I mimiced a Bond one it would already be suited to a villiers 9e. I actually used a Bond minicar one on Bruces Inter and it was loudish but with plenty of perfirmance.

[Jonathan Poll]

Well my dad did make his Nobels silencer out of an old Bond one, and we're suprised how well it goes, my dad was overtaking schmitts on a microcar rally!

I'm not sure if they all have to be tuned to the engine, but I'm sure it helps. Here is something I found of a tuned sports Peugeot moped (of course!) that went 106 km/h (yes, a lot of tuning!), and it shows how he made the exhaust, which doesnt look like it has any baffle in it, so I don't see why the baffle would do anything to the performance (but it will to the sound!).
http://ddata.over-blog.com/xxxyyy/3/95/10/82/106-kmh-avec-un-BB3-SP.pdf

JP

[Barry]

My understanding is that a two stroke expansion chamber should not be restricted in any way.
The idea is to achieve a pulse within the chamber that acts in combination with the exhaust port timing.  The exhaust is developed to achieve maximum HP within a chosen rev range.
Sports exhausts are tuned to give the highest HP which is at high revs at the expense of torque.

Old two stroke port timing was a compromise to give some torque.  
Manufacturing costs prevented fancy expansion chambers.
Villiers engines reving at over 9,000rpm would not last very long.
The exhaust note had to be fairly quiet.

There are a lot of compromises.

If you stick any wire wool in the exhaust you will severely effect the crucial 'pulse' that you are trying to achieve.
Padding is often used against the side walls to reduce the 'crack' of the two-stroke expansion chamber but this effects the 'pulse' within the chamber.

Torque!
More modern two strokes (those that are left) use a reed valve on the inlet to greatly increase torque at low revs.  This option was not available on early Villiers  engines.

If you look at any sports two stroke expansion chamber you will see that the shape of the chamber is a fantastic organic shape normally with absolutely no internal baffle.
The noise reduction is done with a silencer added after the exhaust has done its bit.  Even this reduces power.

I can only quote my Lambretta experience.

Standard quiet clubman exhaust gives 6hp from a 150cc engine at less than 6,000rpm
Big-bore noisier (but acceptable ish) exhaust gives 18hp from a 186cc engine with modern Yamaha's LC350 port timing and reed valve. and max HP at 7500 revs
Fitting a sports expansion chamber would shake your fillings out but increase the Max HP. It wouild be at 9,000 revs and within a more narrow rev range - giving a higher top speed (if the power can match the need).  

Gearing has then become the big issue - you need more than four or if they are close ratio you cant pull away from standing.

So for your application Bob?
You don't want to have a fully tuned high revving power house that you need to play tunes with the gears to get along.
At the same time you don't want to waste power by dumbing down the engine to keep it quiet.
Do you mind having an obviously non standard expansion chamber on there?

You could consider an expansion chamber which mimics modern Lambretta solutions and use a silencer on the end to keep the noise down.
Anything you stick inside will reduce the power because it will effect the pulse.  Use a silencer to reduce noise after the chamber has done its bit.

With the standard port timing and sizes on a Villiers engine, you will probably get the same improvement using just a big bore tube from the exhaust port and use a bigger box for the chamber - stick a silencer attachment on the end.
Don't fill it with wool unless you have to.

Barry

[Big Al]

I think the Bond system you mention, I have one in stash for a car, is a compromise on what Barry has said. It is a budget system so you have the expansion box, a cylinder, and it ends in a baffle. That is the part that creates the harmonic shock wave that is 'tuned'. It offers no silencing so a between that and the end cap/second baffle they put wading in to muffle the noise a bit. If it is the same unit the exit pipe is quite small and angled away from centre to allow the exhaust emission to be angled away from the rest of the car. I assume this system was used as a period motorcycle exhaust would have been to long. Many of these had a built shaped end cap. Silencing was by adjustable baffle of pierced pipe.
The Schmitt silencer which Ian and Russell tuned is a an adaption of the Sachs three chamber system. The important section is the first one which is why the tuned system has a graduated cone enlarging to the fist baffle. The gas slows/cools out. Hits the baffle sending a shock-wave back. This should be timed to aid extracting the next stroke, pulling in more charge as well as aiding more burned gas out. However in its travel back to the cylinder the cone speeds up the shockwave increasing its effectiveness. All this can be done using mathematical calculations but it is not easy.
Anyway the other two chambers take care of silencing. It gives the Schmitt its distinctive deng da deng sound. This remains on the tuned item but the efficiency when fitted correctly is marked.
Modern systems still use the shock-wave but the secondary set of chambers has become the stinger, which further increases efficiency in getting the gas out. Clearly the effort in exhausts is proportional to the state of tune of the engine. For Bubbles the basic is OK as the engines are plodders. In some cases the exhaust is in fact detrimental to the performance for the expedience of quietness. Goggo across the back single system for instance. Replaced on a 300cc by the earlier two box system the car is able to rev and is quicker and cruising speed rises from 60 MPH to 65 MPH (depending on your primary gear set).

[Bob Purton]

Honestly Barry, all you youngsters think about is performance!! I have no intension of fitting any organic shaped expansion chambers on anything! I have the larger bore pipe which is 1 3/4" diameter as used on the later Bonds and Greeves bikes etc, in fact I have bought a Greeves roadster single pipe. As this is for a car I want more power in the lower revs, sorry I wont be joining you as you scream your way down to Southend to fight rockers and smash up deck chairs Barry! From what I have read the consensus is in agreement with what you say about two strokes being better if there is no restriction in the system. As the Bond type silencer is a straight through pipe with just holes in the sides and some wadding around it I cant see how that would restrict any air flow?

[richard]

But surely what you describe sizewise is a silencer for a bond a/b . Haven't we been here before ? 

[Bob Purton]

I remember discussing a Bond pipe but not the silencer. I dont think A or B ones would be suitable as I;m sure the bore would be much to small unless you know differently? Is there a Bond silencer that has an inlet to take a 1 3/4" pipe?

[Barry]

Off to Southend to give those Rockers a good hiding Bob.  They will certainly hear me coming!

Here is a bit on Lambretta exhausts.

http://www.ilambretta.com/exhausts.html


Would look lovely hanging off of your old lump.

[Big Al]

But surely what you describe sizewise is a silencer for a bond a/b . Haven't we been here before ? 

Is it? I must take a picture. Maybe it is not what I want! I thought it was Bond Mk C. There are quite a few Bubble and Scooter versions of a Villiers 197 exhausts, let alone borrowing something from another type of the same cc. I even recall Chevette (?) rear silencer being suggested as an off the shelf exhaust for Villiers and had one on a Frisky that seemed happy enough. Well the Villiers was, I am less sure about the Frisky which went to someone to be loved. I have a brand new one of these auto boxes on the shelf copped at an autojumble at the time.

[Bob Purton]

You may want to sell it to me then Al, not the Chevette one but the mkC one.

[Big Al]

Just locked down that store too. I should be able to reach the exhaust stash. There are various odd items there. Sadly not a Scootacar Mk2 unit but I had thought the unit I had would do until the Scoot could find a real exhaust. A MkA/B will not do this for me. Might finally be able to get at the Crayford too.

[Barry]

And send me that copy of the Crayford Log book too?  No doubt top of your list with the house move..................

A really good photo (or scan) of the chassis plate would be a great help. x

[richard]

a type of bond silencer but this looks  like very restricted outlet for gases doesn't it