How they pass sound regulations?

[dropot2]

Anyone knows how cars such as Ferrari, Lamborghini, Porsche...etc pass the very strict sound regulations???? I doubt that they can pass such a strict tests without doing any trick...electronics maybe?

[gangajas]

By-pass valves? I don't know the exact name.

[dropot2]

Originally Posted by dani_d_mas May be they record the noise at a given rev range... and after that, the noise levels are somehow "free"... but below that they must be lower than a certain level

That's what I also thought, however, even in neutral all that supercars are louder than any current car in the market.

[ZfrkS62]

yes, those flaps in the exhaust tips are on BMWs as well. They are vacuum controlled so at idle and low revs they meet european noise requirements. so i'm sure there is something similar on the others.

[dropot2]

And those flaps are controlled electronically or they are just opened and closed due to the gases forces from the exhaust?

[coombsie66]

There are also differing noise levels permitted for a car that exceeds a certain volumetric efficiency, ie making over a certain amount of power for its capacity.

But the bypass valves in the exhaust, mapped to open beyond a certain engine speed and or throttle position combination would also be a get around used by some manufacturers. Although i believe that in BMW's for instance the valves are also used for all combination of reasons, engine warm up cycle, emissions etc. (i say that as my mums 330 sport has a valve in one of the tail pipes and i can never see when it is open or closed!)

[pitfield]

They are actually mapped to open on more agressive throttle apllication when the carthinks you want it to be noisy.

On BMWs they are for turbo diesel back pressure.

[pitfield]

isn't what you means by volumetric efficiency actually called specific output?

[graywolf624]

And those flaps are controlled electronically or they are just opened and closed due to the gases forces from the exhaust?

Usually electronically. The corvettes for instance are programmed to come open above 3k. Pull their fuse and it always stays open.

[sameerrao]

Well the cars as they come into the dealerships must comply with the prevailing law of the land. All the Ferraris till recent complied to the sound regs - I don't recall what the test exactly is but it involves measuring the sound at idle and also at about 4/5000 rpms. The emissions are also measured simultaneously.

On the 430, they have the bypass valve that literally bypasses the exhaust mufflers and provides a massive increase in sound. Yet it is legal as the laws are defined today.

Aftermarket exhausts for the Ferraris for all the older models normally go with less constricted tubing and are designed for sound quality and slightly lighter weight rather than improving torque/power. In many cases, you can be cited by the cops for excessive noise. These exhaust systems will not really affect the emissions though.

But then some owners bypass the cats and put in test pipes. This is legal in a few states which don't check for emissions. The de-catted cars are reallllly loud and are begging to be caught by cops.

The other issues with aftermarket pipes and cats is that it could prevent the car from being tracked. For example there are many 360 owners with tubis and whatnot being black flagged at Laguna Seca because their cars are too loud. The base cars are borderline acceptable and the aftermarket stuff puts it over the edge. Some of the owners resort to driving past the sound measuring section at low revs to fool them

Kreisseg offers a twin sound system - it has a mildly louder system as stock and at a press of a remote switch, it changes into an F1 like scream that you can hear miles away. Bloody expensive system though - something $8000 - for a fucking exhaust :roll:

[coombsie66]

Originally Posted by pitfield isn't what you means by volumetric efficiency actually called specific output?

Same way of saying the same thing, yeah.