This is determined by a combination of parameters such as exhaust pipe diameter, material, pipe wall thickness, muffler design, flow characteristics, and overall pipe layout.

Let’s start with how exhaust pipe diameter affects performance. Many beginners often hear so-called “experts” say that you should upgrade to an exhaust with a larger diameter than the factory system. But why? In reality, most of these “experts” don’t truly understand the reason. A larger diameter allows exhaust gases to flow more freely, helping spent gases exit the vehicle faster. How does this affect engine performance? The answer is simple: it can help increase engine output to a certain extent.

So, is a larger diameter always better? Not necessarily. Taking straight-through exhausts as an example, only a diameter that properly matches the engine’s displacement is the optimal choice. Once pipe diameter is addressed, another key factor must be considered—low-RPM torque.

Again, using straight-through exhaust systems as an example: their advantage lies in improved exhaust flow at high RPM, making it easier for the engine to breathe at higher speeds and improving throttle response. However, the downside is equally obvious—some loss of low-end torque. This happens because exhaust flow becomes too smooth, resulting in insufficient back pressure. Low-RPM torque is largely determined by engine torque output, and back pressure plays a certain role in supporting that output.

At this point, exhaust routing and layout become critical, as well as whether additional components are used to increase internal exhaust pressure. You may notice that some modified cars overseas run straight-through exhausts but feature unusually shaped piping. This is done by introducing bends in the exhaust to increase back pressure. Some straight-through systems also incorporate a small “expansion chamber” or resonator to alter the exhaust gas path and recover part of the lost back pressure.

For straight-through exhaust enthusiasts, considering these two aspects is enough to begin selecting an exhaust system that truly fits their needs.

Figure: The methods and logic behind exhaust modification are actually quite similar to upgrading wheel and tire sizes. Exhaust pipe outer diameter is measured in inches, not millimeters—this is crucial to remember. Exhaust upgrade planning is usually done in increments of 0.1 inch.For example, if the factory exhaust diameter is 2 inches (about 51 mm), an upgrade would typically be 2.1 inches (about 54 mm) or 2.2 inches (about 57 mm). Going up three steps to 2.3 inches is rarely recommended unless you plan to install a larger turbo later. Based on real-world experience, increasing by one step results in a quieter sound with better torque output, making it more suitable for daily-driven cars; increasing by two steps is slightly louder but not annoying, and leaves room for future ECU tuning.

For enthusiasts who value responsible and civilized car modification, the next key factor to consider is the muffler. Anyone with basic automotive knowledge knows that an exhaust muffler system consists of two parts: the mid muffler (resonator) and the rear muffler.
The mid muffler’s role is not only to provide the third stage of noise reduction (the first being handled by the turbocharger, and the second by the GPF and catalytic converter), but more importantly, to use a larger chamber to allow exhaust gases to expand and slow down, thus reducing noise. What is commonly referred to as back pressure is also generated at this stage due to the reaction force created when exhaust flow decelerates.
Therefore, blindly removing the mid muffler during an exhaust upgrade is neither scientific nor beneficial—it will weaken engine torque output. The phenomenon of “loud but not fast” is largely caused by this mistake.

The primary function of the rear muffler is to eliminate noise produced when exhaust gases exit the system; most of the sound from the exhaust tips is controlled here. What exactly is exhaust sound? Simply put, it is air vibration caused by high-speed exhaust gas flow. If the rear muffler effectively reduces exhaust gas velocity, the exhaust note will naturally become quieter. This is basic physics and not a matter of personal preference.
Because reducing exhaust gas speed is key, various rear muffler designs have emerged. The most common types are S mufflers, H mufflers, and M mufflers.

Let’s start with S mufflers. Most single-exit exhaust systems use S mufflers. Their advantages are excellent noise reduction and some improvement in low-end torque. The downside is less efficient exhaust flow, which can negatively affect throttle response and power output at high RPM.

H mufflers are mostly found on mid-to-high-end vehicles and sports cars. These cars usually rely only on a rear muffler. Their advantage is an attractive exhaust note, while the drawback is weaker noise reduction compared to S mufflers—something that is understandable given the larger engine displacement involved.

M mufflers, also known as variable back-pressure mufflers, feature a valve inside the muffler. At low RPM, the valve remains closed to preserve low-end torque; at high RPM, it opens automatically to ensure smooth exhaust flow. M mufflers are commonly used in valved exhaust systems, where an electric motor allows manual control over whether the valve is open or closed.

Figure: Exhaust products may look simple—something that can be made with a pipe bender and basic welding skills—but in reality, they belong to a discipline that is easy to learn yet difficult to master. Especially in a market where technical products rely heavily on reputation, the threshold for becoming a well-known brand is much higher.

Finally, let’s talk about how exhaust material and pipe wall thickness affect exhaust performance and sound.

The most common exhaust materials are fairly straightforward. Mild steel is widely used due to its low production cost. High-end exhaust systems typically use stainless steel, while top-tier systems may use titanium alloys or feature ceramic coatings. The most noticeable difference among these materials is weight. Generally speaking, stainless steel exhausts are the heaviest, followed by mild steel, with titanium being the lightest.

Pipe wall thickness influences exhaust sound primarily because of exhaust pulse vibration frequency. Put simply, the thinner the pipe wall, the higher the vibration frequency, resulting in a crisper, sharper sound and overall lighter weight—but it also makes the system more prone to exhaust resonance (drone). Thicker pipe walls vibrate at lower frequencies, producing a deeper, heavier exhaust note, and can reduce resonance to a certain extent. The trade-off, however, is increased weight.

It’s important to understand that all exhaust systems produce resonance—the difference lies only in when and under what conditions it occurs. This is why many major exhaust brands use pipe walls that are 2 mm thick or more: to minimize abnormal noises during resonance and reduce discomfort for occupants. Remember, resonance isn’t eliminated—it’s simply reduced to a level that’s hard to notice.

So if any exhaust brand claims that their system has absolutely no resonance, then that exhaust was probably designed for an electric vehicle.

Figure: Titanium exhausts look stunning, but they are expensive. The cost is roughly split between materials and labor—and in some cases, labor can even be more expensive than the material itself.