Exhaust manifolds and headers are two important components when it comes to modifying the performance and acoustics of your car. They play a key role in an engine's exhaust system, and are vital for both improving engine performance and producing a distinctive tone.

What are exhaust manifolds?

In automotive engineering, exhaust manifolds are usually simple cast iron or stainless steel devices used to collect engine exhaust gases from multiple cylinders and transport them to the exhaust pipe.
The most common types of aftermarket manifolds are made from mild steel or stainless steel tubing used for the primary pipe, along with flat flanges and larger diameter collectors that may be made from a similar material to the primary pipe. They may be coated with a ceramic-type finish (sometimes both internally and externally), or with a heat-resistant finish, or bare. Chrome-plated fittings may be used, but these will turn blue after use. Polished stainless steel also discolours (usually to a yellow colour), but less than chrome in most cases.
Another form of modification used is the isolation of standard or aftermarket manifolds. This reduces the amount of heat emanating into the engine compartment, thus lowering intake manifold temperatures. There are several types of insulation, but three are particularly common:

1.  Ceramic coatings are sprayed or brushed onto the manifold and then cured in an oven. They are usually very thin and therefore provide little insulation; however, they reduce engine compartment heating by reducing radiated heat output.
2. Ceramic mixtures are bonded to the manifold by thermal spraying to form a tough ceramic coating with very good insulating properties. This is commonly used in high performance production cars and track racing cars.
3. The exhaust is completely wrapped around the manifold. While this is cheap and fairly simple, it can lead to premature manifold degradation.
4. The goal of a high performance exhaust manifold is primarily to reduce the resistance to flow (back pressure) and to increase the volumetric efficiency of the engine, thereby increasing power output. The processes that take place can be explained by the gas laws, in particular the ideal gas law and the combined gas law.

What do exhaust headers do?

Like exhaust manifolds, headers are designed to direct exhaust gases from the engine to the exhaust system. The main difference is that a header produces less exhaust back pressure than an exhaust manifold, making it easier for the engine to breathe.
Headers are usually made of thin-walled stainless steel tubing. Each header has long, equal-length main tubes that allow exhaust gases to flow more freely than they would through an exhaust manifold.
While some high-performance vehicles come with headers from the factory, most are added as aftermarket upgrades to give the car more power. You'll typically find headers on race cars, hot rods, and other custom applications.

Differences Between Headers and Manifolds？

Let's take a look at some differences between exhaust manifolds and headers.

1. Exhaust manifolds are factory-installed components found on almost all vehicles, while headers are aftermarket upgrades. However, there are exceptions as some high-performance cars come from the factory with headers.
2. Manifolds are much cheaper compared to headers, as headers require careful development specific to the engine they are paired with, and they also use higher-performance materials.
3. Exhaust manifolds are designed by manufacturers to provide a balance of performance, fuel economy, and efficiency, while headers are primarily designed to offer optimal performance.
4. Headers often reduce exhaust backpressure, resulting in improved performance at high RPMs and the associated noise, while exhaust manifolds retain some backpressure to ensure driving performance across a wider range of RPMs and reduce noise.

Can exhaust manifolds be replaced by headers?

Yes, headers can effectively replace the traditional exhaust manifolds in the engine's exhaust system, providing a range of performance advantages. Unlike the single-piece design of exhaust manifolds, headers have separate pipes designed for each cylinder. This design difference allows headers to improve exhaust flow and reduce backpressure, resulting in increased horsepower and torque.

Advantages of headers:

1. Improving Exhaust Flow: The characteristic of exhaust headers is that each cylinder has its own separate pipe, allowing for smoother and more efficient exhaust flow. This reduces backpressure on the engine, enhancing overall performance.
2. Increasing Horsepower and Torque: With reduced backpressure, the engine can "breathe" better, resulting in increased horsepower and torque output. This effect is particularly noticeable at higher RPMs.
3. Enhanced Sound: Exhaust headers can also alter the exhaust note, typically producing a deeper and more aggressive sound compared to the stock exhaust manifolds.
4. Replacing Exhaust Manifolds: Upon installation of headers, they replace the traditional exhaust manifolds. Instead of a single-piece manifold, headers have separate pipes for each cylinder. These pipes then merge into a collector, directing the exhaust gases into the rest of the exhaust system.

Considerations:

COMPATIBILITY: Before installing a header, it is important to ensure compatibility with the engine and vehicle. Headers come in a variety of designs and configurations, so choosing the right one for a particular vehicle is critical.
Installation: Installing headers can be more complicated than replacing an exhaust manifold due to the additional components involved. Often more time and expertise is required, especially if modifications are needed.
LEGAL CONSIDERATIONS: In some areas or with certain vehicle conversions, there may be legal implications to using a collector instead of the factory exhaust manifold. It is important to check local laws and regulations.