Cars make noise. For most of automotive history, people just accepted this as a simple fact of the car world.
There are those in this world who build houses next to major freeways and then complain about the speed of the vehicles going past. There are those who build houses next to airports and complain about the excessive noise.
Just as there are those people, there were those who decided that cars were too loud and needed to shut up!
This presented car companies with a problem. Their engineers were telling them that for maximum efficiency, particularly in the horsepower department, the internal combustion engine needs a free flowing path for the exhaust gasses to escape. To reduce noise, on the other hand, requires a more restrictive path.
For many years, auto manufacturers simply added an exhaust system, complete with mufflers to reduce the sound levels and lived with the horsepower efficiency losses.
The solution for those that wanted the horsepower more than the quiet, was in the aftermarket. There’s an entire industry built around less restrictive exhaust systems.
When noise restrictions, in various guises and rule sets, around the world became extremely strict, this meant that the guy with the loud car was now under risk of being given a defect and put off the road.
At this point in time, a lot of car manufacturers responded by programming deliberate dead-spots into the ECUs of their cars at the particular load/speed points at which cars were tested for decibel loudness, while allowing them more volume everywhere else.
Now we arrive at today and a new solution to the exhaust noise problem is becoming more and more common : Active Exhausts.
What is an active exhaust exactly?
For most car makers, an active exhaust consists of a “flapper” valve that opens up when the driver requires high revs, more response and big power. It bypasses the more restrictive elements of the exhaust. Said restrictive elements stay in play and keep the volume down while running the kids to school or quietly cruising around.
The FPV GT uses a vacuum system where the throttle body pulls the flapper valve open. Other cars, like modern Audis, use a push button on the dash that electrically opens or closes the valve.
The active exhaust provides a simple, elegant solution to getting around the regulations on car noise, while allowing the cars to retain their distinctive exhaust note characters and power production when the need(want)arises.
Congrats to the car engineers of the world for overcoming this problem, but they’re not the first ones to think of it.
Back in the 1930s, American Hot Rodders rigged up almost exactly the same solution by having cable-operated valves that switched between two alternate exhaust systems. These were operated by a simple cable and often jammed in place and had to be re-machined/replaced frequently. But they worked. Perfect for sneaking quietly past that cop on traffic duty before switching over to the noise(and power) maker for the local traffic light grand prix.
Michael Adams from Test Driven Australia
Article Originally Written for Infinite-Garage