Does A Valved Exhaust Alter Engine Performance Or Just The Sound?

A valved exhaust (importantly a different concept than exhaust valves in a cylinder head) is an exhaust system that allows the driver to open or close valves to alter the exhaust noise. Some automakers have put valved exhausts in performance cars right at the factory, but it can also be a "push-to-make-louder" button that you install. The valved exhaust aftermarket is vast, and you can buy the entire exhaust system for your car from anywhere, including specialty high-end custom shops and Amazon.

What's the benefit? Well, a cooler exhaust note is certainly a benefit for a lot of people. After all, when you're revving the engine of your modified Toyota Supra at a car show in a grocery store parking lot, how else is everyone else going to know how souped-up the 2JZ engine is? But is there a performance benefit, as well?

Sort of. BMW notes that the current M5 has "electronically controlled and continuously adjustable flaps" that "summons a rich aural accompaniment to the engine's power delivery." However, the automaker makes no claim toward an increase in power.

Valvetronic, a company that specializes in valved exhausts, states that "the primary benefit remains driver-controlled sound," while also noting that a more open exhaust can reduce back-pressure in the exhaust system. But that's also true of any performance-oriented exhaust system, not just ones that feature a valve. In order for an exhaust system to be more efficient, and therefore more powerful, it has to expel exhaust gases quickly. Valved exhaust systems can help that process, but it's not the only way of accomplishing that feat. 

A valved exhaust can (and probably will) make your car sound a lot louder, and that is an advantage all by itself, especially if you can control the noise. But as for performance, the overall exhaust setup of your car, whether from the factory or a custom build, has more of a say. A valved exhaust certainly isn't going to hurt anything if it's installed correctly, but it also probably won't boost performance much more than a more conventional performance exhaust system would.