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Mark Tearney

Noise limit's..how to test?

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Planning on doing my first track days this year, only had my car a week and have no idea what db's my car is putting out.

I don't want to arrive on track to find I'm over any limit,  how would you go about testing this without having to go to a circuit?

Any advice appreciated.

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If its convenient, get yourself to a track day and get it checked in the paddock before you spend any money. 

Good luck :)

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My nearest circuits are Silverstone or Bedford, guess a drive over to Bedford could be the best answer.

 

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Hi

Bedford seem to work on drive by tests.  From my experience, Abingdon has static tests (100dB(A) at 4,500rpm. 

I am a Motorsport UK registered Environmental Scrutineer and have a noise meter.  If you fancy a run over to Oxford at some point, I could do a test for you.  Alternatively, I will be at the National Kit Car Show at Stoneleigh at the start of May and will have my meter there should anyone want a test doing.

Simon

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Cheers Simon I'm hoping to be at Stoneleigh with luck.

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Would a db level app on your phone be adequate enough to give you an idea of where it’s at?

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Having never used one I've no idea tbh.

Anyone ever used an app before?

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One metre from the exhaust at 45º off the axis and 4,500rpm (or 3/4 maximum revs for a bike engine). Make sure the engine and exhaust are at running temperature. Mine has failed because it was too cold. A quick run around and a retest passed it. This was at MSE Abingdon. I have a really old Tandy analogue gauge which is accurate enough I have found.

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I had the same issue when I replaced the complete exhaust. I tried several apps but this didn't work too well for me. I decided to take it to my nearest track one evening to let the scrutineers measure it. They confirmed the my phone apps were miles away from their readings but then I've got an old cheapy phone...

The worst bit was driving home after being told that the exhaust was fine as I wasn't booked on the session . Oh well 

:cry:

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Or chat to your local council and environmental department..they might do you a favour as you pay their wages!

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14 hours ago, Man On The Clapham Omnibus said:

One metre from the exhaust at 45º off the axis and 4,500rpm (or 3/4 maximum revs for a bike engine). Make sure the engine and exhaust are at running temperature. Mine has failed because it was too cold. A quick run around and a retest passed it. This was at MSE Abingdon. I have a really old Tandy analogue gauge which is accurate enough I have found. 

The distance is half a metre (based on Motorsport UK - MSA before that - regulations).  An extra half a meter between the pipe and the meter would make a hell of a difference.

Warming cars also makes a substantial difference.  My experience of testing rally cars (mainly) over the last twenty years or so is that up to 3dB(A) can be found.  Mind you, to warm a car thoroughly can take more time than you think.  I have oil temperature gauges on two of my cars and they take fifteen miles for the oil to warm up fully!  Other clearances also settle down (transmission, alternator etc).  Obviously, more of an issue for cars that have been trailered to events.

Simon

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54 minutes ago, Simon Marks - North Oxfordshire AO said:

The distance is half a metre (based on Motorsport UK - MSA before that - regulations).  An extra half a meter between the pipe and the meter would make a hell of a difference.

Warming cars also makes a substantial difference.  My experience of testing rally cars (mainly) over the last twenty years or so is that up to 3dB(A) can be found.  Mind you, to warm a car thoroughly can take more time than you think.  I have oil temperature gauges on two of my cars and they take fifteen miles for the oil to warm up fully!  Other clearances also settle down (transmission, alternator etc).  Obviously, more of an issue for cars that have been trailered to events.

Simon

Simon, you are quite correct, sorry! My memory has suffered from too much home brew obviously! I made up a wand with an angle gauge on the end to test mine and it was a mere 500mm long. I've no idea about what aspect of warming is most significant , but I trailer my car to track days so it's stone cold when I arrive. I have to drive up and down the car park for what seems like an age to get it warm enough. If I leave it to idle to warm up not only does it take even longer, but the radiant heat from the (insulated) manifold cooks the alternator (Pinto). Sound measurement is a black art I find and silly things such as being too close to a hard surfaced wall can adversely affect the result and as for hard vs soft surfaces underfoot, well...

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Apps aren’t very accurate. The measuring technique differs from track to track, you’re much better off to go to Bedford (other tracks are available)  and ask them to test it, that’s what I did. Or come to the Cadwell day where the noise limit is very high and get it tested then. 

FWIW IMO a “standard” zetec, with a decent sized and packed can shouldn’t be a problem. 

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Hi, Again,

The 0.5 metre test is a very repeatable test because, as long as you have 3m clear around you, reflection from objects is ruled out.  I once tested a Metro 6R4 in a garage courtyard before a rally.Once at the venue, the 0.5 metre test was repeated and yielded identical results.  You are also testing to a level way above the ambient noise level (typically 50-70dB(A)) so that also has a negligible effect when testing to 100dB(A).

The ground surface can introduce more variables, however.  I assisted at a rally last weekend and we were testing on wartime, tamped concrete.  The Senior Official (who has carried out tests there at many events said that we were to test to a limit of 102dB(A) as, from his experience of that venue, he has to make that adjustment.  The testing on the day found that to work with a good few of the front running cars reading between 100-102, rather than the usual 98-100.  We sent four cars (from 67) away to check over their exhausts befre resubmitting.  My feeling is that it may be due to the corrugations, Mike thinks it may be something to do with vibrations in the slabs of concrete.  Though an Environmental Scrutineer will have a calibrated meter, and will perform calibration checks during the period of a test, local variations will not be ignored and if I were to start a test and the first few cars were all to fail, I would very much be looking at my equipment / procedures rather than send every competitor away.  If the odd cars fail, I tell the drivers that "Exhausts are not like dogs, they are just for Christmas" that can, and do, wear out, or become damaged - or even show the signs of a badly adjusted / about to fail engine.

I am old enough to have suffered the large radius tests, and was threatened with exclusion when my standard (engine and exhaust) BMW 2002Tii recorded a higher reading than the MG Metro 6R4 in the queue before me!  There were gusty winds pushing sound towards the meter and guess who was tested during a gust?

Particularly with rear engined cars, I see various techniques employed by drivers to quieten down their cars at sound tests.  Some hold the clutch down, some will hold the car on the handbrake and bring the clutch up almost to biting point.  These are all possible if people have found them to work. One technique we don't like is people who have switches to alter the reading of their rev counters.  Once you have done a few tests on a morning, you get used to the amount of mechanical mayhem for 4,500 rpm and can soon spot a cheating tacho.  For those without rev counters, I normally take a Snap-On timing light to events and clipping that onto a plug lead gives me a number to work with.

I'm with Archibald Meatpants in that a standardish Zetec should not be problemattical. 

One last point - it is possible to over pack a re-packable silencer.  Follow your manufacturer's instructions and don't be tempted to use up the rest of the roll (or whatever) just because there appears to be room for it in the can!

Simon

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