Most builders in the UK seem to go for a straight-through silencer, mainly because they don't reduce the power too much, but partly because
they're nice and loud and sound impressive! The IVA is also fairly generous when compared to commercial manufacturers. However, the IVA is
tougher than the SVA ever was, and is likely to get tougher in the future. Builders in continental Europe have to meet extremely tough limits. Also,
not every UK builder wants a really loud car.
So my question is - has anyone found a really quiet silencer that doesn't kill the power too much? One that brings the car down close or equal
to regular car noise levels?
Tin-top exhausts are usually oval, with the input pipe going to one side and the output going from the other.
Could this sort of thing be made so that it looks respectable on the side of a seven-alike? Or is there a regular car that has a suitable silencer?
Ah, the Holy Grail of the exhaust world !
Basically anything that silences will restrict flow in some way especially if there are
baffles, perforations, crimps etc.
So unless you use a verrry long straight through options are few........
Unless you stick a turbo further up the line, they damp some noise.
I've got a Yamaha R1 can which is fairly quiet. I got it measured at a Brand's Hatch track day and it was 92db (or should that be dba?)
I couldn't tell you if it reduces power, but seems OK IMHO. Mine's on a 1.4 K series, but I know plenty of other people have R1 cans on
larger engines.
Can on mine is quite quiet, its the TB's that bark louder than a loud dog.
Got it from AAS Newcastle. He asked me how loud I wanted it and said he could make it as loud or quiet as I like.
As stated, the R1 can is probably the best readily available option, nice and quiet and they come up quite frequently on the bay.
It's a 3 chamber design very similar internally to the one shown in your pic. Some have said it's a bit restrictive, but personally I
haven't found it to be so. Look for the one with the carbon fibre sleeve though, apparently the titanium ones will give you probs if you need to
do any welding....
That's true! My bike carbs make more noise than the exhaust - but that could be fixed with an airbox, a long hose and a remote air filter.
I'm talking about a silencer for folk who just want to pootle round the lanes making a nice sound, rather than going for all-out power.
Something that would go through IVA without question, and pass any European country's regulations.
Ideally, it could be home made if the builder is skilled, or made by someone skilled 'on commission' (as 907 does for straight-through
silencers).
Really I'm trying to stimulate forum members to think outside the box... can a good-looking and practical silencer be made that is really quiet?
I'm very interested on this topic! Locost silencer or not.
Please note a different thread I started yesterday: http://www.locostbuilders.co.uk/viewthread.php?tid=137295
Would it be possible to get the 76dbA, even if restricting a lot the car power?
Or, as I ask on the thread, is the stand-still test done under UNECE Regulation 51 different from IVA noise test and thus the 76dbA limit under UNECE
is not comparable with the 99dbA limit on the IVA test?
Please, keep debating; I'm taking notes! 
HappyFather
My straight through silencer was relatively quiet at 96.7 dB. It was very large though and still quite loud really. In back to back tests, I found
the R1 can to be a bit restrictive but lighter than a big straight through can.
I do recall reading that Vizard says if you have an expansion chamber in your exhaust between the manifold and the silencer, it doesn't really
matter what silencer you have, it won't be restrictive. The expansion chamber has to be at least 8 times the volume of one cylinder. I never
tried it.
I have an image in my mind of the 1930's racers with their silencers on the side - they would often have a lozenge-shaped box with an inlet into
the bottom and an outlet near the top - a bit like this one (but it's the other way up and a bit smaller than the ones I was thinking of).
BTW: this isn't for my car - I like being noisy 
- but it is a question that comes up very often, so I was wondering if the Locost collective
genius could come up with something original... something to get away from the bog-standard-seven approach.
[Edited on 4/6/10 by David Jenkins]
Would fitting a resonator somewhere down the line help? They're supposed to make it sound more like a continuous tone right?
http://vibrantperformance.com/catalog/product_info.php?cPath=1021_1033_1054&products_id=288
I've got the basic 'rule of thimb' dims and ratios of volumes for an effective silencer somewhere, as applied to race exhausts at one
time.
As I recall, it all fits into a round silencer about 150mm diam x 460mm long.
I'll try and find it, and let you know.
Chers,
Nev.
if you have an expansion chamber at the front , youll reduce the noise level , you might also increase some back pressure if the chamber isnt long
enough , the start of the AB0 (absorption) part needs to a certain distance from the exit of teh inlet pipe to provide just enough volume to dampen
frequency , but not slow the gas down .
So yes it can be done . you can also go upto 7 inch diameter , weve had good results on an XE powered westie .
i work here
I got a 7 inch can from CBS and can confirm it does drop the sound. Most of my noise is now comming from the carbs.
LINKY
The best designs are straight through with a valve to force the gas around the outer part for quite, or straight through for max power.
Darren
Ok its part to do with his turbo, but speak to Madteg with his zetec, at Stoneleigh you could barely tell the car was on at idle.
quote:
Originally posted by David Jenkins
I'm talking about a silencer for folk who just want to pootle round the lanes making a nice sound, rather than going for all-out power. Something that would go through IVA without question, and pass any European country's regulations.
Ideally, it could be home made if the builder is skilled, or made by someone skilled 'on commission' (as 907 does for straight-through silencers).
If I was building again, I'd be putting a big middle box in the traditional spot by the side panel, and running a pipe round the rear suspension
to a rear mounted silencer. Either under or over the fuel tank.
Something like this:-
Mike
quote:
Originally posted by Volvorsport
if you have an expansion chamber at the front , youll reduce the noise level , you might also increase some back pressure if the chamber isnt long enough , the start of the AB0 (absorption) part needs to a certain distance from the exit of teh inlet pipe to provide just enough volume to dampen frequency , but not slow the gas down .
So yes it can be done . you can also go upto 7 inch diameter , weve had good results on an XE powered westie .
i work here
Turbo's are occasionally called rotary silencers The sound you hear is just energy being dissipated and a turbo is fairly efficient at
removing energy from the exhaust gasses.