Many people think there’s no difference between exhaust manifolds and headers. While both components serve a similar purpose, they aren’t the same. Let’s take a look at the difference between exhaust headers and manifolds.
What Is an Exhaust Manifold?
Most production vehicles (such as commuter cars) have exhaust manifolds installed instead of headers. The manifolds’ task is to collect exhaust gases from your engine’s cylinder heads and transfer these gases to the rest of the exhaust system. Most of the time, manifolds are made of cast iron. This material allows them to withstand the high heat and pressure that comes with exhaust gases.
What Are Headers?
Headers have the same job as manifolds: they route your exhaust gases from your engine into the exhaust system. However, headers are designed with back pressure in mind (specifically, creating less back pressure), which allows your engine to breathe easier and offers a boost in performance.
Most of the time, headers are made out of stainless steel tubing, which is far thinner than cast iron. Headers have equal-length primary tubes longer than manifolds to allow gases to flow more freely. Headers are typically an aftermarket add-on, although some high-performance rides come equipped with headers right from the factory.
Pros and Cons of Manifolds
Most cars have manifolds installed, so what are the pros and cons of the average driver’s engine-to-exhaust system connector?
While cast iron offers more than a few downsides, it’s a thick, sturdy, and durable material that can easily withstand the pressure and heat of exhaust gases. Performance may not be its strong suit, but it gets the job done.
Aftermarket exhaust manifolds move away from cast iron and use stainless steel castings or high-flow ductile iron. Making this quick change can have a significant impact on low-end torque and helps with efficiency while driving.
Another benefit of aftermarket manifolds is their simplicity. They’re easy enough to bolt in and require very little ongoing maintenance— once you’ve got them, they’ll stay solid for years.
There’s a reason manufacturers install manifolds on stock cars: cast iron is the economical option. Unfortunately, cast iron is also prone to cracking over time. Even a small crack in your manifolds is bad news; exhaust gases traveling back into your engine bay are extremely dangerous, and it’s possible for these gases to enter the vehicle’s cabin, as well.
Manufacturers know this, of course, and don’t want drivers complaining that their product resulted in carbon monoxide inhalation. Automakers apply a Band-Aid solution by thickening the exhaust manifolds. This does work to improve the manifolds’ life span, but comes with downsides of its own.
Thicker cast iron manifolds result in less space through which your exhaust gases can pass (the increased thickness is typically applied to the inside of manifolds since fitting larger parts into your engine is tricky). This creates back pressure and slows down the gases, reducing your vehicle’s horsepower and cutting down on efficiency.
Iron casting (instead of the stainless steel you see in headers) is also a rough option. The smoothness of the material has an impact on gas flow— when combined with the thickness of the manifolds, exhaust gases exit your vehicle like snails told to “take their time.”
When the time comes and your manifolds do crack (as far as factory manifolds go, it’s just a matter of time), you may be unpleasantly surprised at the price to address the issue. Factory manifolds are usually proprietary parts designed specifically for your make and model, so most auto shops will need to order the part.
Pros and Cons of Headers
It seems like manifolds have their fair share of problems, but how much better are headers?
The pros of headers are fairly straightforward: they offer far better performance than cast iron manifolds. Stainless steel is smooth and thin, meaning that gases flow much better through headers than manifolds. Plus, each cylinder of your engine gets its own exhaust pipe. This results in less back pressure and faster flow, which increases horsepower and your vehicle’s efficiency.
As with manifolds, the installation of headers is simple. You’ll just remove the old part and bolt on the new one.
While headers offer significant performance increases and cut down on some problems with manifolds, there are a few issues. First of all, because headers are made of a thinner material, noise production greatly increases. If you’re looking for ways to turn your ride into a silent beast, this isn’t it. However, if noise doesn’t bother you (we know quite a few drivers who may consider this a pro), don’t count headers out.
If noise is what you’re after, you may want to consider unequal length headers. Most headers are equal in length (as this option increases performance), but unequal length headers come with a deep rumbling sound and extra low-end torque.
Who Should Use Headers?
With all that said, this is a no-brainer, right? Should everyone go out and pick up exhaust headers to give their vehicle better performance? Unfortunately, it isn’t quite that simple. You’re only going to notice a significant benefit from headers if your engine is high-performance and souped-up to the max. Throwing headers onto a commuter car won’t do much at all.
Many computer-controlled cars will show you a flashing check engine light after you install headers since they aren’t equipped to work with them. An added issue is that most headers don’t have heat shields. This results in an extremely hot engine compartment. If you don’t have other components built to withstand heat, it causes a host of other problems.
Finally, it’s important to note that aftermarket headers are illegal in some states. Before making any purchases, look up your state’s rules and regulations for exhaust systems to confirm you aren’t breaking any laws.
Now that you know the difference between exhaust headers and manifolds, if you have a high-performance car, aftermarket exhaust headers are a no-brainer. They’re easy to install, they improve performance, and they reduce back pressure significantly. Do yourself and your car a favor and bolt on some new headers!