Gentlemen !

just bought a secondhand IXL alloy race silencer and fitted it to ZX9 powered 7 in leiu of a standard can.
Booked in on Cadwell bash in July (hope to see some of you there) 105dB static noise test I think.
Anyway, used my mates (calibrated and hence accurate) noise meter at 1m from exhaust, and made 103dB at 7000rpm (ish).
wondering whether to repack exhaust to try to avoid sailing so close to the wind!.

Question is has anyone got experience / recommendation of which ( if any ) packing performs best , is it worth paying the extra for the more expensive stuff or is it marketing crap?
Any help much appreciated.

Cheers

you can get a db reducer on ebay Item number: 320491209743

I always had one of these in my tool box when I went on a trackday with my bike engined cars with race cans.

http://cgi.ebay.co.uk/UNIVERSAL-DB-KILLER-END-CAN-BAFFLE-KIT-BS-APPROVED_W0QQitemZ270523978729QQcmdZViewItemQQptZUK_Motorcycle_Parts?hash=item3efc7c53 e9

They are cheap,easy to fit and would knock off 4 or 5 db's,I would add that I never had to fit one for Cadwell park,they are not strict with noise there,105 db's is very loud,they do check you at 0.5 metres static though at all the MSV tracks this includes Cadwell.

[Edited on 19/05/04 by PAUL FISHER]

Have a look at this:

linky

I re-packed mine using this and it gave me about a 5dB drop once it had expanded.

Roger

thanks people, Rogers' suggestion is the most appealing since the gas flow is unaffected.

can you let us know how you get on as I might have to reduce noise

You need to repack.... probably (if S/H) not too much glass in there anyway. Makes one helluva difference, I repack before Combe at the start of the season, then it gets noisier as the season develops.
Usually I buy the stuff at Combe:

http://www.merlinmotorsport.co.uk/p1502/E-GLASS-SILENCER-PACKING-1-SQ-METRE/product_info.html

Stuff it in the evening before the event in the paddock and all is well. It's still close, 105dB at 3/4, nature of the beast. If the STV's open up then it's damn noisy regardless.

if you do decide to repack take this advice (Ive done my fair share)
1. There is a difference between 2 stroke and 4 stroke packing. Get the 4 stroke
2. Wrap the center tube very tight with one layer. Wrap this layer with safety wire to hole it tight. Wrap a second layer and stuff it back into the enclosure.

Thanks everybody for help. I followed Roger's link and bought the expanding Acoustifil material.
Repacked can and ran engine up to temperature. Initial reading was similar value to original can packing (which in fairness didn't look too bad once removed !). as engine and can heated up, as required to expand the fibres, a subsequent reading showed a 2dB reduction on the previous. I don't know if the new packing has finished expanding to the full operating volume yet, but would not expect to see much more improvement, will post again if I'm proved wrong !. The exhaust actually sounds a bit quieter and the dominant frequency has changed to a slightly deeper tone.

Thanks everybody for help. I followed Roger's link and bought the expanding Acoustifil material.
Repacked can and ran engine up to temperature. Initial reading was similar value to original can packing (which in fairness didn't look too bad once removed !). as engine and can heated up, as required to expand the fibres, a subsequent reading showed a 2dB reduction on the previous. I don't know if the new packing has finished expanding to the full operating volume yet, but would not expect to see much more improvement, will post again if I'm proved wrong !. The exhaust actually sounds a bit quieter and the dominant frequency has changed to a slightly deeper tone.

I actually bought some of this stuff too on the recommendation of this thread! Any reduction sounds good to me! All the packing has gone in mine now so it is very loud!

Still no engine in the car though so I haven't tested it out yet!

Also just tried some Acoustafil - made a right pong while it was doing it's expanding thing, but now it's 'cooked' it sounds reasonably quiet for a straight thru' box.

Just need to see how long it lasts now......

Just wanted to follow up, tested the can again in accordance with track day testing requirements - 0.5m, 45 degrees...etc. and can performed well. Didn't sound much louder than standard can from memory. So refitted original can and repeated tests @ 6000, 7000, 9000 rpm. Approx. difference was only 2db louder for straight thro' race can.
Best of all though went to rolling road yesterday to have jetting checked - 147.4 BHP @12500 rpm, not bad for a ZX9 well up on previous value !