The sound quality and level of an exhaust is based upon the exhaust manifolds, the exhaust pipe diameter, resonators, and the muffler. The muffler itself is the final element, and is greatly affected by the system design upstream. If you have installed a Flowmaster Super 40 and are not happy with the volume from your exhaust system, you must address other parts of the system or swap the Flowmaster Super 40 for a freer-flowing variant.
Have an exhaust shop remove resonators and replace them with steel exhaust piping. Resonators reduce sound and are used in conjunction with the mufflers to lower exhaust volume. If you look at your exhaust system from the tailpipe forward, you will first see your muffler. Then, as you follow the exhaust pipe forward toward the front of the car, you will see a resonator. The resonator will be a large silencer welded into the exhaust system. The design varies from manufacturer, but it will sit between the catalytic converters and the muffler, typically in the exhaust mid-pipe.
By removing the resonator (two if your vehicle has a dual exhaust) and replacing it with straight exhaust pipe, the muffler will become much more noticeable because the exhaust gas will not being tamed by the resonators. This is your cheapest option, and allows you to choose from a wide variety of resonators to swap with the factory setup if you find a straight pipe to be too aggressive. There will be more resonance from the exhaust, which is a booming sound at low engine speeds. That is the reason exhausts come with resonators.
Install headers, which replace the exhaust manifolds and improve airflow, thus improving power. Thick factory exhaust manifolds cut down on exhaust noise. If you replace your factory exhaust manifolds with headers, your exhaust system will become noticeably louder.
While headers increase both sound and power, they are expensive and can be difficult to install depending, upon your vehicle. If you intend to install headers in the future, you may want put off any exhaust modifications until the headers are installed, as a system that sounds great with stock exhaust manifolds can become overwhelming with the addition of headers.
Replace the Super 40 with a Super 44 or a Super 10 series Flowmaster. You may not modify the actual muffler to increase sound. Cutting into the muffler housing will damage it and void the warranty. The Super 40 is a two-chamber Flowmaster, and is the second-most-aggressive two-chamber Flowmaster muffler behind the Super 44. By swapping from the Super 40 to the Super 44, you will increase the muffler volume.
For maximum sound, Flowmaster makes a one-chamber muffler called the Super 10, which is only recommended for off-road use due to the extremely loud exhaust note it produces.
Both the Super 44 and the Super 10 will increase exhaust sound over the Super 40 without requiring any additional exhaust modifications.
