Cheers, Pewe
Just borrowed a sound level meter and i'm pushing 110dB WITH the dbkiller exhaust inserts (dual carbon bike cans) (10k max rpm, 7500rpm test)
Any good ideas how to significantly reduce noise - or any cheap silencers I could fit instead of the bike cans?
James
[Edited on 17/2/09 by cloudy]
what type of bike cans?
some are louder than others....
Make up a butterfly restrictor - (basically a steel circle with two butterfly wings cut out and bent upwards near the centre) to wedge in the
tail-pipe - it can always fall out after the test!
Cheers, Pewe
Just been through all this, Got 108dB on my test. Finally got it through (cbr954) by doing the following.:
Fitted airbox and lagged the engine bay with accoustic foam probably wont help you. Basicaly I lost 13dB by killing the enine bay noise
I don't have an engine bay! Already have inserts marmot, original airbox fitted!! I need something more drastic...
James
Could I set my adjustable limiter to 8500rpm, sign a change form to put max power at 8500rpm and be tested at 6375? Comments? I'd be upfront as
to why
James
create a large wooden box that the exhausts vent into, baffle and allow a small vent to the real world.
Should kill it nicely (wood so it doesn't boom & large box to slow down the exhaust gasses)
Completely made up idea but it should work
Which bike cans do you have fitted?
Phil
generic carbon cans from a VTR I believe...
James
no chance of getting away with putting a lower limit, the form clearly states revs at which maximum power is developed, not what you want it limited
to, be a good idea though
tony
i know in the olden days of SVA they used to use the instrument rpm. Not sure if they still do. Could be worth telling your rev counter that its a 5
cylinder engine ....... 
Although you'll have to practice looking surprised and then worried if you've over reved the engine on the way to SVA.
Are they race or road cans? Road cans from something like an R1 may be considerably quieter.
Phil
There's no way the max rpm can be 10k if the engine can only rev to 8500rpm!!!
quote:
Originally posted by mad-butcher
no chance of getting away with putting a lower limit, the form clearly states revs at which maximum power is developed, not what you want it limited to, be a good idea though
tony
Just a couple of questions
Is you noise meter properly calibrated ?
Did you do the noise test as per SVA regs ?
Mike
yes and yes...
James
Right.
Looks like you've *bags* of space at the back of the car there
Suggestion: what about 2 more in-line silencers linked into the existing system using flexipipe...
Ally Thunderace cans are quiet.
The one below was loaned out to a mate for SVA at Norwich. 86db's on a cross flow.
They are 60mm inlet, hence the mod to 2" i/d
Paul G
Rescued attachment IMGP1447-s.jpg
we always used to shove steel wool up the exhaust pipes on the rally cars for scrutineering. They have become wise to this recently though and making sure we have something secure to keep it in place. can always work its way loose again later on!!!
An over-reading tachometer works well.
Of course the best option is to plan well from the beginning and build a V4 with twin pipes... 
i guess half your trouble is mechanical noise from the fact you have no engine cowlings. i read somewhere that there was a system/method of testing
which took this into account but i cant for the life of me remember where i read it 
quote:
The Two Metre Static Test: The meter is placed at 2 metres away from the centre of the car at a 90 degrees angle to the side of the car. The driver will be asked to rev the vehicle to 3/4s of it maximum engine revs.The reading will then be taken. This test usually only used if it is suspected that mechanical noise is giving a false reading. Rear engined car for example.
I,ve used coarse wire wool as well for MOT's on my open can bike for the MOT, pluck out your DB killer and back fill the cans out of site of the
tester, that should kill the noise nicely for a few pennies and no hardship.
It will blow out when you remove the DB killer, any little strands that may still lurk inside will soon burn off.
Regards Mark
[Edited on 21/2/09 by mark chandler]
Is that an SVA rule?
I've ordered some wadding to put behind the push in baffles, see where that gets me, if no go then it's onto the suggestion of
changing/swapping the cans...
I suspect you are all right, it's mostly mechanical noise from the block itself...
How likely is it that slightly biasing the rev counter would be noticed by the tester?
James
Wadding will be very restictive, may even stop the car running as it will bunch up behind the can, very coarse wire wool is favorite.
[Edited on 21/2/09 by mark chandler]
OK I've bought some coarse steel wool to try