Exhaust Manifold Buyer’s Guide
- Exhaust manifolds vary in terms of design, size, and material. Each one is designed to suck as much exhaust gases from the cylinder, a process known as scavenging.
- The job of the exhaust manifold is to collect the gases and guide the flow through the catalytic converter, the muffler, and exit via the exhaust tip.
- The exhaust manifold reduces the chances of exhaust reversion by preventing the gases from rushing out of the chambers.
- The exhaust manifold is bolted directly to your car’s engine block and is the head section of the exhaust system.
- Cast and tubular manifolds are the two common types of exhaust manifolds.
- OE exhaust manifold replacements on CarParts.com can cost you from $9 to $1,300.
Among the things you’ll initially see upon popping up the hood are intertwining, snake-like tubes attached to the engine. This set of tubes is called the exhaust manifold and is referred to as the lung of your vehicle. That’s because the exhaust manifold is where the exhaust gases are exhaled through. Exhaust manifolds vary in terms of design, size, and material. Each one is designed to suck as much exhaust gases from the cylinder, a process known as scavenging. Some exhaust manifolds are even designed to concentrate the heat of the gases to burn the uncombusted fuel.
How does an exhaust manifold work?
As you may know, air enters the engine through the air intake system, which is composed of the air filter and intake manifold. On carbureted vehicles, the air and fuel meet inside the carburetor, while on most modern vehicles, the fuel injector sprays fuel as air passes through the intake manifold. The same air then gets combusted along with the fuel, creating exhaust gases that initially contain toxic substances.
The job of the exhaust manifold is to collect the gases and guide the flow through the catalytic converter, the muffler, and exit via the exhaust tip. It also prevents intake reversion, which happens when there’s backpressure in the exhaust system or when the system becomes too restrictive of the cam. The backward flow of exhaust affects engine performance as leftover exhaust leaves less room for a fresh air and fuel mixture. The exhaust manifold reduces the chances of exhaust reversion by preventing the gases from rushing out of the chambers.
Where is the exhaust manifold?
The exhaust manifold is bolted directly to your car’s engine block and is the head section of the exhaust system. The connection point between the engine and the manifold is sealed by an exhaust manifold gasket. The position varies depending on the engine bay’s layout and the car model. You may find them bolted directly on top, on the side, the front, or sometimes on the rear of the engine block. You’ll easily spot them as the tube often sticks with long large, intertwining tubes.
Types of exhaust manifolds
There are different varieties of exhaust manifolds in terms of design. Different types affect engine characteristics in various ways. To understand exhaust manifolds deeper, let’s take a closer look at the different types and designs.
Cast Exhaust Manifold
Cast manifolds are the most common type you’ll see in most cars as they are relatively cheap and easy to make. However, there’s a drawback to being inexpensive. The short-tube design of cast manifolds causes a restriction to the engine by allowing interference between the cylinders.
Tubular manifolds solve the interference problem in cast exhaust manifolds by featuring individual pipes per cylinder. This design isolates the gases so they don’t interfere with each other. Tubular manifolds can be made of steel, stainless steel, Inconel, or titanium. There are two configurations of tubular manifolds: the 4-2-1 and the four-into-one. 4-2-1 exhaust manifolds feature two pairs of pipes that merge toward the end known as the collector, while four-into-one manifolds have all four individual pipes joined together.
Symptoms of a bad exhaust manifold
Louder engine noise
If you notice that your engine got louder than it used to be, you might be facing a problem with your exhaust manifold gasket. A faulty gasket can cause a weird sound from the leaking exhaust gas. You may hear a hissing or tapping sound when your vehicle is accelerating or when starting your engine on cold weather.
A decrease in power and acceleration
If the exhaust manifold fails, exhaust gases could leak out of the pipes. What’s even worse is that the gases also have a tendency to be sucked back to the chambers and cause reduced air-fuel mixture. Less fresh air and fuel inside the chamber means less power. This could affect the acceleration and the pull of your vehicle.
Poor fuel economy
The decrease in power also affects your car’s fuel efficiency because low power means your engine needs to work extra hard to perform the task. The harder your engine works, the more fuel is required in the chamber. As a result, you’ll be spending more on filling up your tank on a regular basis. Fixing the exhaust manifold might sound costly but at least you won’t spend more on fuel in the long run.
A burnt smell coming from the engine
Since a cracked exhaust manifold causes exhaust gases to leak, plastic and rubber parts around it could burn. The exhaust is hot, and long exposure to it could cause surrounding non-metal components to burn. If this happens, you may start smelling burnt plastic and rubber odor, especially when your engine heats up.
Strong gasoline or diesel odor
Exhaust manifold leaks cause a strong fuel odor that may enter the cabin. This is because of the leaking exhaust gases coming out from the damaged pipe of the exhaust manifold. The gasoline or diesel smell could also indicate that your vehicle’s fuel consumption has been compromised due to a bad exhaust manifold.
How much is an exhaust manifold?
Aftermarket exhaust manifold replacements on CarParts.com can cost you from $9 to $1,300. The price range includes single-piece exhaust manifolds as well as sets and kits. To get the perfect fit, you may indicate your vehicle’s year, make, and model on the filter tab under the search menu. You may also narrow down your search by choosing from the categories under the “Shop By” section.
When choosing an exhaust manifold replacement, take note of your state’s emission standards. On CarParts.com, exhaust manifolds are categorized by their emission standard-compliance. There are products that are legal in all 50 states, while there are some that are only legal in 47, 48, and 49 states. Before you purchase an OE exhaust manifold replacement, do your research regarding your state’s emission law.
3 Critical Things to Consider When Buying an Exhaust Manifold
Exhaust manifolds are usually made from porous metals that expand and contract depending on the temperature. This makes them more prone to cracks over time. Once your car's exhaust manifold breaks, the engine's performance will be affected because of the unequal air-to-fuel ratio. Also, harmful exhaust gas will leak into the car's interior, putting yours and your passengers' health at risk. This is why a damaged exhaust manifold should be replaced immediately. If you're in the market for a replacement part, you should consider these three critical things so that you won't regret your purchase.
OEM or aftermarket?
OEM manifolds are typically made from cast iron, so they are inexpensive. But because of production cost constraints, some OEM manifolds are susceptible to rust and corrosion. Aftermarket exhaust manifolds, on the other hand, are engineered for optimum engine performance. They can be made from stainless steel, coated mild steel, or aluminized steel. However, aftermarket manifolds are more expensive than OEM.
Exhaust wrap, ceramic paint, or ceramic mixture?
Proper thermal insulation is essential to help prevent overheating inside your car's engine bay. Below is a list of the most common types of insulation used on an exhaust manifold.
- Exhaust wrap: This type offers excellent insulation because it's wrapped completely around manifolds. Though it's relatively cheap, it can cause premature manifold degradation.
- Ceramic paint: Usually sprayed or brushed onto manifolds, ceramic paint reduces the heat through radiation but not that much.
- Ceramic mixture: Because of its very good thermal insulation, ceramic mixture is commonly used on performance cars and race cars.
Stainless steel, aluminized steel, or cast iron?
If you're having a hard time choosing the best type of exhaust manifold, here's a list of the advantages and disadvantages of the common types of manifold.
- Stainless steel: This kind of exhaust manifold is rust resistant. It can also retain its chrome-like shine for a long time. However, despite these benefits, stainless steel manifolds are more expensive than other types.
- Aluminized steel: By forming a layer of oxide, aluminized steel prevents corrosion. Although it's cheaper and lighter than stainless and cast iron, it easily rusts once the oxide layer is scratched or dented.
- Cast Iron: Stock exhaust manifolds are made from cast iron, so they are affordable. However, they tend to be on the heavy side, and they don't boost engine performance that much.
Replacing a Damaged Exhaust Manifold
The exhaust manifold directs all the exhaust gases from the engine to the exhaust system. Without it, poisonous exhaust gases will reach your car's interior, and the car's engine will be damaged. If your car's exhaust manifold is damaged, you have to replace it immediately. This guide will show you how you can replace it without visiting a mechanic.
Difficulty level: Moderate
- New exhaust manifold
- Torque wrench
- Socket wrench
- Floor jack
- Jack stands
- Rubber mallet
Step 1. Park your car on a level surface. Then, lift up the front part using a floor jack. Don't forget to place jack stands under your car to make sure that it will hold up.
Step 2. Locate the exhaust manifold. It's usually attached at the engine and the exhaust piping.
Step 3. To remove the manifold from the exhaust piping, use your socket wrench to unscrew the bolts holding it in place. Then, remove the exhaust pipe from the manifold.
Step 4. Remove the bolts attaching the manifold to the engine with your socket wrench. Depending on your car's engine, the manifold may be secured by eight to 12 bolts.
Step 5. Gently tap the manifold to free it from the engine cylinders. Then, completely remove the exhaust manifold.
Step 6. Make sure that the new exhaust manifold, exhaust piping, gaskets, and cylinders are clean to install the new manifold properly.
Step 7. Attach the gasket on the new exhaust manifold. While making sure that the gasket is in place, slide the new manifold into the cylinders.
Step 8. With your torque wrench, screw the bolts attaching the new manifold to the cylinders.
Step 9. Attach the new manifold to the exhaust piping, and screw the bolts with the torque wrench. Your car now has a new exhaust manifold!