INDY BIRD
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| posted on 16/8/06 at 06:14 PM |
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Help! need to reduce Decibel readings
Hi
I have fitted a new 7" stainless can to reduce noise levels but even with this large can i am getting readings of 101 db.
this is at 45 deg - 500mm from the exhaust as they test at track days,
it seems that the can is quiet and the engine is making the noise around 106db at 500mm.
so the question is where to go next to get it under 100 db or less.
can i insulate the engine bay if so with what material any reccomended?
or any other suggestions greatly appreciated.
This is on a blackbird engine if any help.
i have tried other exhaust like the R1 can this reads 102db.
pic of exhaust fitted.
[Edited on 18/8/06 by INDY BIRD]
 
Rescued attachment 7 exhaust.jpg
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Jon Ison
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| posted on 16/8/06 at 06:34 PM |
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what air box you got, induction kicks out a LOT of noise, my intake is 2" behind my head and trust me its loud.
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TangoMan
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| posted on 16/8/06 at 06:56 PM |
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I had a similar issue.
My answer was to build an airbox and wrap the exhaust manifold.
This made a fair difference. I am now at 99db so still a bit more to do ready for Donington.
Summer's here!!!!
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smart51
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| posted on 16/8/06 at 07:36 PM |
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does wrapping the exhaust manifold make much difference?
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INDY BIRD
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| posted on 16/8/06 at 07:42 PM |
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i am running a tts full flow filter.
i tested with airbox and without it makes approx 1db reduction.
so still some way to go will look at wrapping the exhaust next if it helps??.
do you think if i sound proof the engine bay this will help or is it unrealistic to get a bike engine car under 98db.
cheers
Sean
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The Shootist
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 posted on 16/8/06 at 08:51 PM |
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Outlet direction...
You might gain some room by turning the exhaust down toward the ground.
Also check all exhaust/engine mounting points for stiffness. A mount to sheet metal could cause a ringing amplification.
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givemethebighammer
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| posted on 16/8/06 at 10:03 PM |
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quote:
Originally posted by The Shootist
You might gain some room by turning the exhaust down toward the ground.
Not for Donington, the sound bounces off the track and reverberates between the walls on the pit straight - been there, pipe straight out to side
(not pointing down) gives a lower reading.
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Jon Ison
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| posted on 16/8/06 at 10:14 PM |
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That's one of the reasons Ive gone too great lengths to get mine pointing out the drivers side.......................
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givemethebighammer
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| posted on 16/8/06 at 10:17 PM |
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quote:
Originally posted by Jon Ison
That's one of the reasons Ive gone too great lengths to get mine pointing out the drivers side.......................
I can't win, 4 carbs sticking out of the bonnet on the drivers side and the exhaust the other. Finally decided that a bigger silencer and an
airbox are the only things that will keep me driving at Donington.
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Jon Ison
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| posted on 16/8/06 at 10:34 PM |
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quote:
Originally posted by givemethebighammer
quote:
Originally posted by Jon Ison
That's one of the reasons Ive gone too great lengths to get mine pointing out the drivers side.......................
I can't win, 4 carbs sticking out of the bonnet on the drivers side and the exhaust the other. Finally decided that a bigger silencer and an
airbox are the only things that will keep me driving at Donington.
in that case you will have too induce a spin as you go past the noise meters keeping the exhaust and carbs away from the meters.........
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MkIndy7
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| posted on 16/8/06 at 11:25 PM |
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Ahh now we know why F1 cars have their air intakes above the drivers heads, and the exhausts coming out of the middle of the car,
To pass the noise restrictions at Donnington!
I alway thought it was to do with Aerodynamics 
Do they stop the planes taking off while they noise test you?
(not sure how they measure that one but I think Concorde was only 112 db when the Americans were monitoring it landing when it 1st went over  )
And just to shoot myself down in flames a normal Passenger jet is only about 72db
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givemethebighammer
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| posted on 17/8/06 at 08:38 PM |
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quote:
Originally posted by MkIndy7
Do they stop the planes taking off while they noise test you?
Do they 'ell,those Russian transport planes are louder than four sevens put together, I'd like to see the marshall black flag that one in
!
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INDY BIRD
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| posted on 18/8/06 at 05:38 PM |
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Any other suggestions welcome.
or is it impossible to get a bec under 98db????????????????????????????.
I would like to get under 100db to be on the safe side for evening sessions.
Cheers.
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TangoMan
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| posted on 18/8/06 at 08:30 PM |
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With a 7inch can I think your exhaust will be fine. An airbox will help more if you duct teh inlet from inside your nosecone.
The other possibility is to line your engine bay side panels with some kind of foam rubber. This should absorb some of the engine noise. Obviously you
will need t be aware of exhaust heat causing you a problem
I am not sure how much difference wrapping the manifold makes but it can only help!!
Summer's here!!!!
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ChrisGamlin
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| posted on 20/8/06 at 04:18 PM |
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Someone on the BEC list lined his Westfield engine bay with (I think) fireproof insulating mat that you sometimes use in sidepods etc, and it had a
positive effect. You can also try looking for any bare ally panels that may resonate and try damping them by sticking rubber mat or high density foam
sheet to them, as that can also have a significant effect.
Its entirely possible to get a BEC down below 98db though, a friend's blade with a 7"x30" Raceline can and open filter was measured
at something like 94db at an airfield day.
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