Have a guess what this is the noise level of? Yup, my exhaust @ 3500 revs in neutral! And I plan to go on a trackday on saturday with a 98db limit.

So, tomorrow evening I am going to nip down to my local friendly exhaust place and we're gonna play with cats / boxes to see if the noise can be brought down a bit....

Damn, I never knew it so bloody lound. Just glad I bought a meter from Maplins tonight and didn't find out on the day!

just to make sure you know the test is done at 45 deg from the tip at a range of 1m

just to make sure you know the test is done at 45 deg from the tip at a range of 1m

So 45 degrees upwards from the car at 1 metre? Hmm, I was a lot closer, but I don't think half a metre will make much difference.

Thats loud, who is your exhaust man because i want my cat cut out.

Also too loud for the ring iirc.

OK - It seems perhaps the meter is not right for the job. I have measured it at the usual 45 degrees and 1 metre and it is still around the 105+ mark. However, the gauge reads dbC, which apparently is totally unfiltered. The track should use a dbA meter, which will hopefully give a lower reading. Kind of wish I'd known this before buying this but I have never had an exhaust which is this loud, and never had a moment like this where it could be seriously bad,

I am going to test some more stock exhausts tonight to see how they compare noise wise, and shall use that as a guide.

I hope you were wearing ear protection at that level :P Thats not much different from a pnuematic road drill, your neighbours must love you, or you had the meter too close.

So 45 degrees upwards from the car at 1 metre? Hmm, I was a lot closer, but I don't think half a metre will make much difference.

It may make quite a bit of difference... in a good way.

Moving the meter out will bring the SPL down.

Edited 25 February, 200917 yr by Mr Wobblytickle
had the wrong end of the stick

Just had a quick look on goooooooooogle, there is a big difference in filtering at lower frequencies between dbA and dbC so hopefully that will make a marked difference to the value.

According to the HSE website your car is somewhere between road drill and chainsaw. Apparently a reduction in 3db is equal to halving the noise level.

Yep DB is exponential so at around 105db each extra db is about twice the noise level.

Also remember that the meter is measuring every surrounding noise aswell. Also warm weather gives lower readings to cold weather.

My race bike used to measure 1db less if i stood next the the bike when noise tested over sitting on it as my body whould sheild alot of mechanical noise from the engine itself.

I'd want it to be nicely below 100 dB though, that's plenty loud enough for street use realistically?

dBC isn't entirely unfiltered but dBA does cut the lower frequencies much more severely, so it should register a lot less :

its also illegal for road use as maximuim db is 74. which came in about 10 years ago.

its also illegal for road use as maximuim db is 74. which came in about 10 years ago.

At what distance???

So where have you got that from???

Road Rally's are restricted to 98db @ .5 metre from exhaust and they are well below the legal limit.

My standard Opel Manta made more than 74db:eek:

Simon

Edited 25 February, 200917 yr by mantamad

So for a car, what would a 110 dbC reading relate to in dbA I wonder? Looking at that chart, it would suggest that if the frequency of a diesel exhaust is 100hz, that would knock my 110dbC down to 90 dbA. I feel like I want to risk it, but the dbA meters from Maplins are very expensive!

those maplin spl meters are rubbish jason, i've got a calibrated one that i use at work and it shows a massive difference in reading to a cheapo one, at a disco the other night it was showing 126dB on the maplin el cheapo one, and 121 on the calibrated one

Do you use the C frequency for that? I noticed it said that it was for use in office environments, etc. No mention of motorsport, etc. If I can be fairly sure the frequency is low enough to give a sub 98 dbA reading, then I am happy to no bother modifying my exhaust....

Have a look for a MSA scrutineer in your area as they have all the gear that has been calibrated ect and will know what they are talking about. Ask your local motor club and may be join.

simon

Just go to a different trackday perhaps?

Devonutopia post a video or sound clip somewhere it sounds bad a$s! I want to hear it in full tune

At what distance???

So where have you got that from???

Road Rally's are restricted to 98db @ .5 metre from exhaust and they are well below the legal limit.

My standard Opel Manta made more than 74db:eek:

Simon

http://ec.europa.eu/environment/gpp/pdf/toolkit/transport_GPP_background_report.pdf

doesnt say the distance, ill have another look at Road Vehicles (Construction and Use) Regulations which the police use on boy racers later as its hidden way in there somewhere.

Castle Combe?

Im a local.

You can rent bolt on mufflers that just clip on the end, try phoning the track, or Merlin Motorsport, who are based on the track side.

HTH. Dave

its also illegal for road use as maximuim db is 74. which came in about 10 years ago.

That's for construction type approval purposes. In that the manufacturer can't make it louder than that or it won't pass TA.

Historically you aren't allowed to modify the exhaust by removing baffles and gutting the boxes or cutting the exhaust short to remove boxes. It's also not legal to remove anti-polution gear. Initially aimed at VTA breathers. A large percentage of the total emmisions can come from the breathers, and that's at lower revs! Same legislation can apply to decatting. It's just that local Police and councils etc don't tend to bother.

Designing and implementing a whole new system with improved parts is a different matter.

Whatever the arguments, having a car that's arguably too loud to use on a trackday is tending towards the "taking the p*ss" side of things.

J.

Looking around now for somewhere with a dbA meter. Tried a couple of local garages which are involved in motorsport.

Hoping that the derv exhaust is quite a low frequency, at least when compared to a petrol, and that will bring the volume well under 98dbA.

Bloody scared me with the dbC meter reading though! I used it in the car at a set of traffic lights on my way to work this morning. 103dbC just inside the cabin alone! :eek:

110dB is very very loud, can't see your fbaia being anthing like that TBH Jason, my cobra without the silencers in obly just that level

ALex