Exhaust Manifold
Comprehensive Guide :
What is an Exhaust Manifold?
An exhaust manifold is a metal chamber that houses the escape of the exhaust gases from the engine’s combustion. The exhaust manifold is the first step the exhaust gases take to exit the engine, it is also the first component of your exhaust system. The exhaust manifold is also a key component that is a part of making your engine efficient. Exhaust manifolds also can be known as headers aid in getting rid of waste from your engine’s combustion (exhaust gases).
Depending on how efficiently these gases flow out of your engine and how the flow of pressure is used will determine how efficient your engine will be depending on the engine’s applications. Stock headers try to strike a balance between efficiency and being cost-effective, hence the design of the manifold will reflect that. This article will give you a deeper understanding of how this component works and why its design is important to your engine’s efficiency.
How Does an Exhaust Manifold Work?
As mentioned above, an exhaust manifold houses the escape of the exhaust gases from combustion. It is designed with particularly shaped pathways for these gases to travel right after the piston has forced it out of the combustion chamber. Certain aspects of the design of these pathways can affect the way the gases flow. Aspects such as a smooth surface, a bigger pathway, as opposed to smaller ones, or even the length of a pathway, can determine how efficient other parts of the exhaust system can be. Each cylinder has one pathway to dump exhaust gases which the manifold houses into one unit. All pathways lead into one central tunnel that then creates pressure to push out exhaust gases even further.
In naturally aspirated engines there is something called exhaust scavenging which is the back pressure that naturally builds in an exhaust manifold, which is then used to make the process of combustion more efficient. As the exhaust valves open to let out the exhaust gases, naturally a pressure builds to suck the exhaust gases out this pressure returns in a negative form and then enters the combustion chamber changing the pressure levels. This pressure level makes it ideal for the intake portion of combustion, helping to suck in the air/air-fuel mixture.
Materials and Construction of Exhaust Manifolds
Common materials used for exhaust manifolds are Cast Iron and stainless steel. Cast Iron is more commonly used by manufacturers because it is more cost-effective, it can be made compact and in large batches while stainless steel aftermarket headers have to be made one at a time. Cast iron exhaust manifolds have high thermal properties that can withstand temperatures up to 1500 degrees Fahrenheit. Stainless steels are mainly for aftermarket headers because they have an even higher heat capacity. Headers are also very customizable which allows you to pull more power from your engine.
You will usually find OEM manifolds made from cast iron. Cast Iron manifolds have the benefit of being shorter and compact which is good for engine packaging. Another benefit is that it allows any turbocharged cars to spool up faster due to the short distance of the pathways to the turbo. These short pathways also mean that there is less surface area to dissipate heat, which means this heat gets to the turbo and catalytic converter quicker to produce less emissions while being more efficient for engine power.
On the other hand, stainless steel headers can operate at temperatures above 1700 degrees Fahrenheit making it ideal for performance/race applications. Stainless steel is stronger than cast iron so less material can be used overall for a similarly sized and designed manifold making it lighter while being stronger. Stainless steel is also pretty customizable, the exit pathways (runners) are longer than cast iron manifolds so you can play with the efficiency of how the engine breathes. It also has a smoother finish than cast iron making it easier for exhaust gases to flow through.
Types of Exhaust Manifolds
Stock Exhaust Manifold – These are factory exhaust manifolds that come with your car. It is usually made of cast iron for its cost-effective, Thermal, and efficiency metrics. Cast iron exhaust manifolds have great thermal properties operating in temperatures up to 1500 degrees Fahrenheit. They can be made in bulk quantities and are shorter in design which helps with being efficient. The trade-off vs an aftermarket header is that the design of cast iron manifolds is usually more restrictive while headers offer a more custom free-flowing design.
Aftermarket Headers – Headers do the same job as an exhaust manifold however, headers usually come with longer custom pathway designs. Headers produce a better way for exhaust to flow out of your engine which is great for engine power. Headers come in different sizes and configurations such as an equal length, or an unequal length, which speaks to the length of the exit pathways (runners). Different lengths and sizes of the runners influence the engine power early or later in the powerband. Headers are also made of stainless steel which has higher thermal properties than cast iron. The point of headers is to find a custom setup that can pull more power out of your engine by increasing the flow of exhaust gases.
Common Issues and Maintenance
Common issues with exhaust manifolds are cracks, leaks, and gasket failure. As your engine operates the metals get hot and expand and once the engine is off it has time to cool down and contract. These constant changes can create cracks or leaks in the manifold depending on the age of the car/parts, wear and tear status, or quality of the materials.
To know whether or not you have cracks or any leaks here are some common symptoms :
- Noisy exhaust (hissing sounds, whistling sounds. popping sounds).
- Clicking sound from the engine bay.
- Reduced power, performance, and efficiency.
- Burning/exhaust smell in the cabin area.
- Check engine light.
Usually, if you have any cracks, leaks, or gasket failures in your exhaust manifold to best course of action is to diagnose and have the manifold replaced if need be. Prices for manifold fixes can be between $200 – $500 depending on the severity of the leak.
Engines and Their Relationship with Exhaust Manifolds
Your engine is a pump simply put. To get more power it depends on how well air flows in and out of the engine. The exhaust manifold is the start of how well the air flows out. Depending on the engine configuration or application your exhaust manifold design will either be restrictive or more free-flowing. Naturally, aspirated cars depend on a certain level of backpressure for a scavenging effect, to help in the process of combustion, whereas turbocharged engines do not. The design, size, and length of the runner are what determine scavenging as well as the efficiency of airflow to a turbocharger.
FAQ
1. What is an exhaust manifold, and what function does it serve in a vehicle?
An exhaust manifold is a piece of metal that is the first part of the exhaust system. The Manifold attaches to the cylinder head of an engine block and is designed to collect and guide the exhaust gases from engine combustion out of the system. The exhaust manifold is the first step of exhaust gases exiting the engine.
2. What materials are commonly used to manufacture exhaust manifolds?
Commonly used materials for exhaust manifolds are cast irons for their high thermal properties. Other materials used are stainless steel for its higher heat capacity and are mainly used to make aftermarket headers.
3. What are the common signs of a failing or damaged exhaust manifold?
Common signs of failing or damaged exhaust manifolds are:
- Clicking sounds from the engine bay
- Burning/exhaust smell in the cabin area
- Reduced power, performance, and efficiency
- Check engine light
4. How does an exhaust manifold differ from an exhaust header?
An exhaust manifold is the base cast iron housing that is on your engine from the factory. It is usually good for efficiency in spooling up turbos and less emissions, however, it is usually more restrictive in airflow. A header is an aftermarket more free-flowing custom-designed housing meant for the efficiency of air flowing out your engine which gives your engine more power and is usually made of stainless steel
5. Can a damaged exhaust manifold affect engine performance or fuel efficiency?
Yes, a damaged manifold can affect engine performance or fuel efficiency. A part of a manifold’s job is also to create a good seal while providing an exit pathway. If this seal is cracked or damaged in any way it would mean that the engine is not getting good enough compression to flow out exhaust resulting in the engine working harder which increases fuel consumption and engine power being wasted.
