Would it be.sto keep it on [Racing] to allow exhaust with less back pressure for better fuel mileage/less air pollution?
Registered tree-hugger and Greenie wants to know.
Thank you.
There is what they call an active exhaust valve in the exhaust system that opens up more on different settings or when you floor the vehicle. On my challenger I have a setting for auto mode, custom, sport mode or track mode. with those settings I can also change steering feel, suspension and traction.
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Has a quiet mode along with normal, sport, and track mode. Just opens or closes valves in the exhaust to control the volume of the exhaust.
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Happy Birthday wolyrobb
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Used to be you had to get out and use a wrench to open up your laker pipes to make your exhaust louder. Now the car does it for you.
Another way to hear musical sounds from cars
The electronically actuated valve system must be expensive to replace. The option price from the factory is $1225 on the GT.
What an odd way to spend money.
But to each their own. 
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I have driven on the one in Mex Mexico, it was cute, but not real neat. Maybe with a unicycle, but with the front and the rear wheels both sounding the thump, well… I drove it with my Ram truck with its long wheel base and in my wife’s Toyota with its much shorter wheel base and it sounds better in the Toyota as the two notes (front and rear tire thumps) blend a bit better…
A radio station played a couple of these road-produced tunes the other day, true, not exactly high fidelity. The other problem they noted is that since the music’s key (pitch) varies car to car, a group of cars makes for an embarrassingly “out of tune” sound, a nearby residents complaint.
Quet mode is a result of one of the head engineers for Ford having the neighbors complain when he started up his GT350R. Quiet mode measured at 72db at idle compared to 82db in normal or 84db in track mode.
The Ford Mustang’s Active Exhaust Modes (cjponyparts.com)
I personally think the GT350R sounds absolutely brilliant. Especially about 7000 rpm! That flat plane crank sounds nothing like my cross plane crank engine.
I might still want an active muffler for highway trips.
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Agree with Mustangman that flat-plane crank Mustangs sound amazing.
An additional note on valves in exhaust systems: When you see a BMW with two exhaust pipes right next to each other, one of them has a vacuum-actuated butterfly valve in it. At low throttle, the butterfly is closed, forcing the exhaust to make an extra loop through the muffler to scavenge condensed moisture out of the muffler. At WOT, water evacuation is not a concern. Volume is also not a concern, so the butterfly opens and the exhaust gas takes the path of least resistance. As for failure, the only failures I have seen are cracking of the rubber sections of the vacuum hose that runs the length of the car. I expect that corrosion is also a problem in some climates. They tend to fail open so no one worries about it too much.
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Are you referring to the exhaust sound loudness? It seems like the designers would be more concerned with the loudness at WOT than at idle. Can you clarify?
I recall a BMW with that exhaust system. Customer complained that there was a faint, tinny, rattle sound on cold start that lasted 5-8 minutes. Finally traced it to the butterfly at the muffler, it would rattle cold and tighten up when the exhaust warmed it up. I believe that muffler was upwards of $1400, so the customer opted to live with the rattle.
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Some 1970’s era 5L Ford engines had a temperature-controlled butterfly valve in the exhaust system. I think it was used to direct heat to the intake manifold when engine cold to improve HC emissions. My Ford truck doesn’t have it, but the repair manuals suggest it is a pretty common failure item for vehicles that do.
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