Buzzer

I think my thread re: Exhaust System Price comparison has been hijacked and is possibly a little over my head.

Could someone please give me the db outputs for the usual back boxes such as:

Scoobysport (janspeed)

Haywood & Scott

Firestorm

etc etc

I believe the legal limit to be 88db. I would also be interested in knowing what db increase a de-catted centre section would make to the said exhausts.

Cheers

AND DON'T FECKIN HI-JACK THIS THREAD

hades

What kind of reading are you after? I've got a spreadhseet with some readings from america, which are 20" behind the tailpipe in a straight line at 5000rpm held in neutral. I've also got some from the UK at 1m, 45º behind the tailpipe, on a concrete surface at 5000rpm (which is approximately what they use for SVA, where the limit is something like 103dB IIRC). Some circuits have limits for "drive by" which are of the order of 90dB, which is taken a few metres away from a car driving past often floored in 2nd or 3rd, I believe. Obviously drive bys include other noise such as tyre rumble and induction roar.

nom

In general, I think decatting the centre increases the level by 3db, a resonator only making 1-2db difference (reduction if you have one in, that is ).
DP can be up to a 9db increase, the quietest being the BPM at, I believe, around 3db, although I'm not convinced...
I think you're after something in the middle, yes?

The only way to work out what you actually want, unfortunately, is to 'try it out'. Although of course other owners can help here . The problem is that different noise levels are different to different people, if that makes sense
I can't stand noisy exhausts, which gives me a very limited selection . The easiest to live with - although this is a classic which is considerably noisier - is the Drager. Perfect noise level, to my ears. Deep but not noisy, nor unpleasantly throbby at motorway speeds like most.
As for noise levels, I think the only place that actually note them are ScoobyWorld. There was/is a comparison on a US - I think - site, but it's all stuff that's unavailable here
There's the APS stuff as well that gives a noise level.

stiler83

There are some readings-levels on www.scoobyworld.co.uk under their exhaust section.

Buzzer

Hades / Nom

Thanks for that, well noted.

Stiler, i have listened to those but what i would like to know is how the Police detect you exceeding the regulated sound limits (which i believe is 88db).

Okay so they may pull you over and say "Your exhaust seems a little loud sir"

and you say "Well **** yes, so what"

How does the Copper atain whether you are within the permitted sound barriers.

Pete

nom

I don't think they care unless you're obvious
I'm twittering along at around 109db at the moment (and not enjoying it the things we do for flow, eh? ) and have been followed here & there by police. But then I've driven like a limp thing & they've gone away. This is the noise level that sets of car alarms (had fun in LHR terminal 2 car park doing a floor at a time ) but they don't seem to care.
So just don't go nuts & they won't mind would be my thoughts.

Buzzer

What exhaust are you running nom ?

nom

It's not very standard. As in not very 'off the shelf'.
The only bit that is is the Afterburner backbox, which is a 3" jobbie with a (not sure) that Hayward & Scott changed for me Actually, that means the BB isn't an off the shelf one either... oh well
Hmm. The centre's standard, actually. A 3" tube with a couple of bends in it
Noisy "£^"£%"%
Very one-off manifold doesn't help, either .
If you want noisy/free-flowing, the 'Pat Spec' is the one you want. 3.25" - largest anyone so far can mandrel bend Wasn't available when I got mine jigged.
I'm waffling. Sorry

hades

Nom - I thought the new APS racing exhaust thing was 3.5" and mandrel bent? (not bent very much, admittedly). Anyway, I digress.

If you're being nicked against an exact limit, they'd have to reproduce the conditions specified in the limit, use a calibrated sound meter etc to make it stand up in court. However, I believe they have the right to pull you based on "believing it may be" - i.e. their judgement.

"Limit of 88dB" is pretty meaningless until you specify the conditions under which it is measured. Most standard cars on the road would probably exceed that figure if you are measuring the sound pressure in the tip of the exhaust pipe under full acceleration. Move the measurement 10 metres away, and drop to tickover, most modified cars would pass very easily.

To give an idea of the sort of detail you'd need - the test for SVA approval, IIRC, states something like:
Not more than 103 db(A weighted) at a distance of 1m from the tip of the exhaust, at 45º from the axis of the exhaust. Measurement taken on a concrete surface, at 200mm above the surface or the centre line of the exhaust tip, whichever is lower. Car to be holding steady at 2/3rds of maximum power revs.

Sorry if that's getting a bit techie!

Buzzer

LOL Hades

I think you and nom have answered the question admirably. It would be safe to say that the Police would not really be overly ar5ed with trying to nick someone for exceeding sound emission limits however it would also be safe to say that if you were persistantly travelling a route in a built up area very early am the chances are someone is gonna get really pi55ed with you setting their alarm off and thus complaining to the law

Cheers guys

anyone know what a Firestorm kicks out then

Abbylad

iTrader: (4)

Full Firestorm de-cat system is 104dB iirc

Edited to say actually thats an Afterburner system that is 104dB

[Edited by Abbylad - 7/24/2003 5:49:34 PM]

nom

Ah, 2.5" it's 103db.
3" set-ups are quite a bit louder (and never seem to be listed).
I think that's probably why the Blitz, Hiper, etc. are always louder than most, is that they are 3" without saying so. Which is probably a good thing

Buzzer

Abylad

Can you give me the link to that report please mate

scoobyDAZZA

i was led to believe that to double ur noise level u had to gain an extra 3db
ie 97-100 doubles the sound
if 88 is the legal limit then 109 must be f**kin loud


agrees with every one who mentioned scooby world

the centre section will increae it by roughly 1db

ive got the blitz centre and bb,,probably 3db(double) more than standard

daz