noise, inside and outside

[purple charlie]

looking for opinions and info.
my C4 1987 has twin 3 inch pipes, previous or previous previous owner fitted them with silencers. So, over 10 years they have been on the car . The new section 59 laws are supposed to be tightening up. whats the chances they are picked up . I do tend to drive quietly , I'm not a boy racer... any thoughts, don't really want to buy a new system as these are solid and Ive just retired...

second question, the radio does not work... that's not the problem, I wouldn't be able to hear it anyway. The exhaust does sound loud in the car, sometimes have to have windows open as makes it quieter, when the motor is pulling, under load, the droning exhaust is louder. Anyone recommendations on noise deadening the underside of the car?

 

[Chevrolet]

Does the car still have the "Y" pipe at the back that goes into the backs of the exhausts/mufflers or silencers as you call them? If not, previous owner may have bought/fitted aftermarket "straight pipes" you could get that run straight from the manifolds to the silencers, bypassing the catalytic converter? More power/more noise?

 

[purple charlie]

not really had a good look under, only seen under at the mot and was looking elsewhere but cant see a Y piece, or cat, just a pair of mufflers under the trunk

 

[Roscobbc]

Certainly sounds like a previous owner has junked the original system and replaced it with something aftermarket. If the mufflers are a bullet shaped unit perhaps they may be of a 'straight through' design. These rely on internal wadding to deaden the sound. This is often glass fibre which can deteriorate with age and can get noisier. Why not go to an exhaust centre that deals with American cars and replace them with something new and quieter?

 

[teamzr1]

I do not know what the UK demands as to maximum sound output in DBa

I did a lot of testing as to exhaust design and sound output in DBa for my C5

In short get a sound meter that can report sound in DBa
Placing the meter at right angle measure to muffler tips like at idle to start with

My findings shown below as you can see the design of my exhaust and type of Bullitt muffler I choose
Here in the USA that do not want DBa over 85 as you see in my chart
You want the sound Dba even lower in drivers area
Sound bounces off ground and underside of car making it louder inside
The further downstream you place the exhaust tips the less sound bouncing so will lower DBa inside
as I have shown you can buy sheet of sound reducer that has an adhesive for easy installing and that will reduce the sound bouncing and lower sound level inside the care
In my case measured at muffler tips at idle was 105 DBa
With the changes I made above dropped sound level to 85 DBa and dropped to 74 DBa in drivers area
Tips were moved downstream 3 inches beyond rear fascia and end to end exhaust used 3 inch pipe and inlet and outlet of mufflers also 3 inch connected to 3 inch collectors of long tune headers

I temp installed 2 mica phones, for each muffler tip and recorded testruns to measure outside and another mic inside to record sound levels

Decibel Exposure Time Guidelines

Accepted standards for recommended permissible exposure time for continuous time weighted average noise, according to NIOSH and CDC, 2002.
For every 3 dBa over 85dBa, the permissible exposure time before possible damage can occur is cut in half.

Continuous dB Permissible Exposure Time

85 db 8 hours
88 dB 4 hours
91 db 2 hours
94 db 1 hour
97 db 30 minutes
100 db 15 minutes
103 db 7.5 minutes
106 dB 3.75 min (< 4min)
109 dB 1.875 min (< 2min)
112 dB .9375 min (~1 min)
115 dB .46875 min (~30 sec)

 

[Steven Smith]

Section 59 of the Police Reform Act 2002 does not target loud exhausts directly, but police can use it if excessive noise contributes to anti-social driving that causes alarm, distress, or annoyance.
What it does cover:
Nuisance activities such as revving engines, wheel-spinning, street racing, or riding quad bikes/off-road bikes in parks and footpaths.
It has always been there they have just removed the warning part and can immediately seize a vehicle.

I think you would have to give them good cause first.
My 86 has previously had the cats and mufflers removed so it is straight piped.
I have gradually been fitting internal sound deadening matting.