which exhaust (silencer) to reduce noise?

[Comadis]

i need to reduce the noise of my 1700cc x-flow engined kitcar.

it has a tubular manifold which ends in 1 standard silencer (120mm diamter, around 800mm long).

i m searching a silencer which has around the same dimensions (could be a bit bigger and longer) but needs to be quiter or maybe "adjustable" to de- or increase the noiselevel.

also an idea would be a re-packable one, but most i´ve seen are longer. any idea?

[wiz 1]

Wunoff exhausts 6" repackable s/s got mine fitted to my westy over christmas delighted with it and so much quieter than the factory box, very good chaps to deal with as well.

http://freespace.virgin.net/wunoff.cpe/sport.html 

Edited by wiz 1 on Monday 10th March 20:34

[Comadis]

how "heavy" is the silencer and what you paid for it?

have checked the homepage and the noise result test: seams a bit too loud!!

need between 75 and 80 dba on around 4000rpm

Edited by Comadis on Monday 10th March 21:52

Edited by Comadis on Tuesday 11th March 13:03

[Sam_68]

How is the noise level to be measured?

Normal practice on UK race circuits is static measurement at 75% maximum revs, measured 0.5m/45 degrees from the exhaust exit, in which case you are going to have real difficulty getting a Crossflow with a 'sidewinder' exhaust down to 80 dB(A)... mid-90s dB(A) is more realistic and highly tuned crossflows on twin Webers often struggle to stay the right side of 100 dB(A)!

[Comadis]

..its a tuned x-flow, stage 2 head, 1740cc...with twin webers.....

anyway...i need the noise reduction for our MOT here not for a trackday:

normally (officialy) its measured by driving past a noise-level meter. arriving with speed 50km/h, than pushing full throttle in 2nd gear in both directions and also in 3rd gear in both driving directions. measuring distance is around 7metres for 50m on a special noise-reduced tarmac. so you end with 4 measured noise levels taking the average out of these.

for my MOT tester it´s "only" necessary that i´ve fitted a differnt silencer than now and it must be quieter than the acutal one (..a very loud one). sure i wont get the noise level down to the requested 85...but if it sounds a bit quieter than i guess i would pass the test, too.

Edited by Comadis on Tuesday 15th April 20:22

[Sam_68]

OK. That's not so bad - obviously noise level at 50 metres is not nearly so stringent as measurement at 0.5 metres; also 50kph is not a very high speed, so you the engine won't be turning so fast.

Unfortunately, it will be difficult for any UK forum members to advise you, since our only real experience of sound testing is the static test at 0.5 metres applied at race circuits.

[Comadis]

lol...the 50 metres is the length of the test-track.

distance is about 5 metres

Edited by Comadis on Tuesday 15th April 20:38

[Sam_68]

OK. Even so, the noise level readings will bear no relationship to the 'British' test static at half a metre...

[Comadis]

but your test is for trackdays, only i guess?...ours is for the mot.

[andynoquantum]

I've had good results from my local Powerflow dealer. They're franchised, and I've also heard shock stories from people who havent been so lucky

Might be worth looking into, failing that - exhausts.uk.com

[wiz 1]

Heard these are pretty good available in 5" or 6". Really rate the Wunoff though similar spec and price.

http://www.cbsonline.co.uk/5-stainless-steel-silencer-sil5-438-p.asp 

My original Westfield silencer 41/2" didn't have any baffles or packing, sounded ok for a while then had to use ear plugs. Must have been well over 100db. Still got through UK mot.

[Sam_68]

Comadis said:

but your test is for trackdays, only i guess?...ours is for the mot.

Yes, understood.

What I'm trying to point out is that you are unlikely to get any valid advice on what type of silencer is likely to meet your noise requirements, because the few people on this forum who have any experience of noise testing Crossflow engined kit cars will have been using a completely different test methodology.

Tuned Crossflows on twin carbs tend to be quite loud, so they are likely to be pretty marginal on any modern noise test. No one is going to be able to tell you: "If you fit XYZ silencer, it will be very quiet and will sail through any noise test", so you will need data taken using identical testing methods, for it to be of any real value.

[Comadis]

what you think about using such a thing:

http://www.cbsonline.co.uk/bolt-in-silencer-baffle...

this system is well known for motorbikes as well

[CorseChris]

Switched from a 4 1/2" Westfield silencer to a much newer 6" re-packable one and it transformed the noise level. The extra volume of the can made all the difference. Can't give any figures as I never measured it, but the difference was very significant. Anything that gives you a bigger volume is going to help. I've tried a similar sort of insert you linked to before and they didn't really seem to do very much. Safest to say fit the biggest 'can' you can find I think.

Facing a noise problem on my Strat replica at the moment. Far too loud for my taste at the moment. I intend fitting a much larger volume silencer as soon as I can get round to it.

[blitzracing]

You could try a Jetex decibel tube insert. They simply bounce some shockwaves back and take the "bark" out of the exhaust, but dont restrict the gas flow significantly. Don't cost a lot either. Merlin Motorsport do them.

[Comadis]

have tested now a db-insert and made a static-test (same principle used here than in uk---but static is not engouh, the "real" test is by driving as described above):

90db at 4000

also tried 2 small silencers in a row plus the db-insert: same!!

so how the hell i can cut down this level to around 80- (maybe) 85db?


by the way: the db-insert reduces the engine-power to half (on my enigne). as the gas-flow is reduced so much i would not recommend to use them for longer rides. i would be afraid to "overheat" my exhaust valves.

Edited by Comadis on Tuesday 15th April 20:25

[Sam_68]

Comadis said:

so how the hell i can cut down this level to around 80- (maybe) 85db?

80 dB @ 4,000 rpm on a tuned Crossflow with a side exit exhaust?

You're having a laugh!?

Remember that the decibel scale is logarithmic; a reduction of 6dB is equivalent to a halving of the sound energy, so you're talking about needing silencing that's more than twice as effective.

From my experience, I'd say that there's no readily available silencer that will give you that sort of reduction. You could try a large diameter (6&quot repackable alumnium job, but I wouldn't bet on it even getting noise levels down to the mid-80 dB range.

If you're going to stand any chance at all of silencing down to those sorts of levels, you'll have to satrt thinking of ways to reduce other noise; wrap the exhaust headers, heat mat under the bonnet, fit a decent air box and remote filter to the carbs, etc. to limit as much mechanical and induction noise as well as the exhaust.

...but my Elan produces more noise than that with a mildly fruity rear-exit exhaust, and my tuned Crossflow Sylva (with a large diameter repackable silencer) creates more than 80 dB at idle!

[Comadis]

...i guess thats the reason why the german seven-designers route the outlet of the sidepipe above the rear axle to a a 2nd silencer which is plassed across the rear of the car.....to remove it after the mot-test was done....stupid laws....!!!