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Discussion Starter · #1 · (Edited)
== DRAFT: Appendix to original article: http://www.digitalcorvettes.com/forums/showthread.php?t=145093 that includes additional information ===

In addition to lighting constraints, ECE Regulations also stipulate the maximum amount of noise a car may produce; these noise rules are designed with the pedestrian in mind.

The basic idea is that a car that is driving normally in a densely populated area should not bother pedestrians; such as those having an espresso on the side-walk or just enjoying the view in Paris, after a hard day of work:






So the law is that a passing car, driving at city speeds, should not produce more than:

  • 80dB if registered for the first time before 1990
  • 77dB if registered for the first time between 1990 and 1996
  • 74dB if registered for the first time from 1997 to this day

When not specifically stated, noise levels are provided for a stock US 2008 Corvette C6 Auto Z51 with a 6.2L engine. The dynamic noise test for this car gives 87dB; a stock US Corvette Z06, 7.2L, produces 91db.

Bearing in mind that every increase of 3dB is equivalent to doubling the amount of noise ... that is seriously over the legal limit and a lot of noise to get rid of.

High performance vehicles such as the Corvette have a tolerance of 1 dB in addition to the 1 dB given for lack of precision in the instruments; another 1dB tolerance is given for inclement weather. As such a Corvette can slide through at 77 dB if the inspector is in a good mood.

There are two tests that are performed: static noise measurement and dynamic noise measurement.

Static Noise Measurement:

The static noise measurement is a reference value used to see whether or not the car has been modified since the last legal test. There is no legal limit for the static test, it is a pure reference point for any law enforcement officer doing routine street controls.
The microphone is placed in the axis of the exhaust, at a distance of 50cm (19 inches) from the tip. The engine is revved at 75% of max RPM. There are a few variations of this scenario that are sometimes done but these are not of importance in my mind because there is no limit ... so who cares?

If the exhaust tips are slanted (downwards or upwards) the microphone is placed in the axis of the tips. This was initially defined for trucks but once the maximum noise level was set to 74dB, manufacturers started turning the tips of the exhaust away from the microphone, for the dynamic test, to gain a few decibels.

For example, here is the exhaust of a French car that is oriented downwards:



Instead of straight out exit:



Note: in the case of the Corvette there is a protection, when no gear is engaged, that limits revving at 4 000 RPM. This is noted on the car papers, in my case, it is noted [email protected]

Now this value is used because a LEO can pull you over, ask you to rev at 75% of max RPM and measure the amount of noise your car produces. If it is over the limit officially registered ... you are in trouble ... in the best case you get a heavy fine ... in the worst case, you walk home because the vehicle is impounded. :thud:

Dynamic Noise Measurement:

This is the tough one and where many people have great difficulties.

The test is as follows and executed on normalized asphalt:

  • Car cruises at 50km/h (31mph). This is most common city speed limit (25mph in the US)
  • Start of measurement zone reached. The car goes WOT in third gear (third gear engaged before entering the zone).
  • End of measurement zone reached. End of WOT for the car

The picture hereafter illustrates the general layout of the test:



Are measured:

  1. Exit speed
  2. Max noise produced in the measured zone

The measurement zone is 20 meters long (21.8 yards): so the car goes WOT over that distance.

Two microphones are placed halfway (10 meters from start of WOT), off axis by 7.5 meters (8.2 yards) at a height of 1.5 meters (4 feet and 11 inches).

The most noise the car is allowed to produce at this test is 74dB so as to not inconvenience pedestrians. 74 dB is the amount of noise you have in any restaurant with people talking ... which is to say not much. :WTF

Dynamic noise testing has shown that three elements produce the major part of the noise, in the case of my Corvette:

  1. Car tires
  2. Exhaust noise
  3. Engine noise with air intake

Driving at 50km/h (31mph) with stock GoodYear RF Summer tires inflated at 30 PSI, the car produces 64dB of sound; the engine at this speed is inaudible.

Going WOT, the major part of noise increase comes from the air intake and the exhaust.

Noise from the engine and tires can be reduced, as explained here: DIY - C6: Sound and Heat insulation

Some countries within the European zone are more or less stringent on the 74dB sound limit. In France, for a high performance vehicle the limit is 77dB and, unless you have connections, it is stringently enforced.

In Switzerland, there is an additional constraint that is imposed where the Corvette fails: air/fuel ratio on a cold startup. Apparently the Corvette, on a cold startup, has a air/fuel ratio which is too rich resulting in failure of the test.

It is therefore necessary to program the ECM to have a more lean startup in order to be compliant with Suisse regulations. In France I did not have this issue, except for the noise, the car as I converted it, was compliant straight out of the box.
 

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Interesting write-up Fluff. Great pictures too! :thumbsup:
 

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Discussion Starter · #3 ·
Just took some pictures walking from the office one day for the guys on DP Review. :thumbsup:
 

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Must be nice to work in that environment. The only thing missing are those scantly clad womenz! :D
 

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Discussion Starter · #5 · (Edited)
Front Tow Hook

I do not know if this a Euro regulation requirement or a French requirement, in any case, in France a car needs to have a front tow hook that can be removable.

I am not sure about the driver behind this requirement, however it is there.

Not having the ability to weld a removable tow hook and at the time I didn't find many solutions, I purchased and installed the Pfadt racing hook which meets minimum requirements.

Pfadt Racing Tow Hook




Since then the market has improved and it is easy to find removable tow hooks. For example: EZ C6 Removable Front Tow Hook.
 
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