A combination of going past a noise meter in a group of noisy cars, upwind, and a backfire on liftoff resulted in tripping a driveby noise meter by 0.7db and getting a black flag at Bedford yesterday. The engine is currently between 92 and 95 Db static at 6k rpm.
I currently run a big reverie air box and large can (MK Indy can, hayabusa engine).

The Javelin organisers were unwilling to let me back on, despite the circuit staff offering to let me try some different exhaust wadding. Although the car has had no problems at this circuit before I have donington this weekend and would like to know if there is anything else I can try. What do you think? Was I just unlucky or should I try something else? My current airbox seems to work really well instead of a naked air-filter, and I don't really want to do anything which would affect the engine map. My short list is below.


Block off pair valve to reduce backfiring past noise meters (will it affect engine map)
Exhaust filling change (will it make any difference, any recommendations)
Exhaust bung (will it affect map)
Move air box ram air intake from bonnet to RHS (will it affect map?)
Swivel my silencer to point the exit under the car, as it currently points right at the noise meters(would scrutinisers like this)
Put an aluminium floor under the engine for aero and to also reduce noise escaping out of the bottom of the engine bay.
Short shift past noise meters and ask how close I am to the limit, stating that I am moving my shift point up throughout the day but don't want to get too noisy (but in doing so attract more attention to my car)
Short shift past noise meters without speaking to the track staff and just hope for the best, then just go all out in the last session of the day to see if Its too loud once I have had my money's worth!

Thanks in advance!

I would create some sort of turn-down for the muffler and short shift. I've read of several people having good luck with this method.

If you can easily change the intake to point the other way I would do it. Its surprising how much noise is generated from that side of the engine.


Do you have any pics of your intake? Unless you do something dramatic I would think that the effects would be minimal.

One of the big issues at doni for becs, other than the stupid noise limit, is that the one sound Meter is on the pit straight above the wall, and as the exhaust exits this side it screws you. I only ever do unsilenced days there now as been kicked off too many times. If you don't normally have issues at Bedford and you suddenly have now I'd repack your exhaust as its probably blown or melted the wadding. You could also get a decibel killer baffle in you exhaust for doni as an added precaution

[Edited on 24/2/13 by MK9R]

A nice sensible car engine may well solve all your problems.

No, I'm not being insensible here. Having had so many drive-by issues at Combe, things went Zetec silver top instead of GSXR1000. I now have no issues anywhere, in addition the static test (2,500 rpm instead of 9,000) is a farce.

The complaining undead probably can't hear it above their mobility scooter whine.

Thanks for the input, hopefully will get to the bottom of it. Good point about a car engine but I'm not interested in another 80kg of weight, sorry. MK9R, will they let you back on at donington If you fit a db killer?

Here is the current airbox setup. The engine was mapped at PDQ tuning as is, but I have an additional carbon adapter shown in third picture. If I fitted it to the airbox it could take a feed from a hose to a ram duct at the front or RHS of the car instead rather than the top of the bonnet...but then i'm worried about affecting the map, and whether it would improve it. Another option would be to cover the exposed top of the airbox in soundproofing, but again, really worth it?







I also removed the silencer wadding to show this- now I know next to nothing about silencer filling - but it doesn't look particularly good, being just a thick crude layer. It was particularly tightly packed leading me to think that It would tend to deflect the noise and let it carry on down the pipe rather than be absorbed into the can. is that correct thinking, and I wonder if acoustafill or similar would be better to repack with?

Hey,

I've just had an exhaust fitted by AB performance, and they've used the acoustafil as the choice of wadding. Apparently very good at reducing exhaust noise.

As for the airbox - an inlet pipe would help reduce the induction noise, obvioulsy making sure it doesn't effect inlet airflow too much. With regards to the ecu mapping the effect would be minimal.

From the pics it looks like the airbox is open? where's the filter?


C.

Ok thanks, have ordered some acoustafil.

If you look at picture 2 the filter is actually a large reverse cone located inside the bulbous round part of the airbox, you can actually just about see it. So any induction noise needs to go through one box, into the next, and then through the foam and bonnet. So I wonder if having a 100mm induction pipe to an air intake at the front or RHS would make any difference?

I am loathe to make too many adjustments at once because you then never find out what actually fixed the problem, but If donington are prepared to let me make adjustments I might take a naca duct and hose along just in case... so does anyone know?

[Edited on 25/2/13 by Custardpants]

My mistake, does help if I look at the pictures properly!

I will be installing a NACA duct and intake pipe in the nose cone. how much difference that makes - i have no idea!

For reference for anyone else - have looked up the Donington Noise management plan. In theory according to the rules a blanket one strike and you're out noise track ban isn't the case - they do appear to give you the chance to make one more alteration to your exhaust / induction to try to get you back out;


5.1. If DPR is of the opinion that any vehicle does not comply with the applicable noise limits for it will require the organiser to prevent such vehicle(s) from continuing to use the Race Track unless such vehicle(s) can be modified to be re-tested and thereafter comply with the noise limits.

5.3. Vehicles exceeding the relevant drive-by limits will be allowed to undertake repairs and modifications including the fitting of improved or additional silencing and in doing so provide evidence to the Noise Control Officer of the works undertaken. A vehicle may be re-tested once. If the vehicle fails the second test it will not be allowed back onto the Race Track.

I was given another chance and fitted a DB killer, but then got kicked off first session out.

That wadding looked fecked. Just ordered some acoustafil myself, not tried it yet but hoping for good results. If you can route your exhaust to point the other way somehow it would really help.

Acoustafil is really good, it should make a huge difference!

I did a test on the acoustafill to try to work out how much is needed. It appears to be approx. half what the online calculator on the acoustafill site says. First pic i used a hot air gun on an offcut inside some in a baked bean can. The material itself is far more pleasant to handle than fibreglass and doesn't really give you any splinters. The weave itself is very densely sown together with strands which appear to melt quickly with heat to release the other fibers to expand to their original size.



Then I filled my silencer approx 70% with acoustafill and took the car out for 40mins. During the drive I could really smell it going off. Once it had cooled down enough I pulled the material out to take a look and see how it had expanded... despite my test I'd still filled the can too much - It was still a fairly dense but impressive solid mould of the inside of the silencer, It really does have impressive expanding properties. I have since repacked with a bit less, and hopefully will get better results. My very unconventional 'add on' bike silencer/passenger warmer is also nearly finished.

Knackers filled mine tonight with the amount the calculator stated
If not taking it out now, just hope its below 105 db

quote:

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Originally posted by MK9R
Knackers filled mine tonight with the amount the calculator stated
If not taking it out now, just hope its below 105 db

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I just repacked my silencer with with that stuff last week and on my carbed blade with no CAT got 96 @ 7k last Thurday if thats any help and I don't have and air box either.

This stuff seems have worked, my car was only 100db, the quietest its every been. It has got quieter after the first race, it obviously needs a good blast to heat it up and expand it.

quote:

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Originally posted by MK9R
This stuff seems have worked, my car was only 100db, the quietest its every been. It has got quieter after the first race, it obviously needs a good blast to heat it up and expand it.

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