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What Is a Manifold?

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  • Written By: Dan Cavallari
  • Edited By: Bronwyn Harris
  • Last Modified Date: 18 June 2014
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    Conjecture Corporation
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Automobile engines are complex pieces of machinery with countless moving parts that facilitate combustion, which provides the power by which the vehicle moves. Two important pieces of this puzzle are the intake manifold and the exhaust manifold. The intake manifold is a pipe (or pipes) that supplies a fuel/air mixture to the cylinder where combustion takes place. The exhaust manifold collects exhaust from the cylinders, moves it into one pipe, and sends it toward the exhaust system. Both systems improve the engine's efficiency and power output.

Intake manifolds are usually made of aluminum or cast iron because these materials are resistant to high heat. More recently, composite materials have been used to manufacture intake manifolds. The purpose of the intake manifold is to provide the correct fuel/air mixture to the cylinders, which in turn promotes better engine efficiency and even more power. Because intake manifolds create a vacuum — that is, the air pressure inside the manifold is much lower than that of the earth's atmosphere outside — it can be used to power other elements of the engine or outside units such as the power steering or windshield wiper units.

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Exhaust manifolds serve almost the opposite function of intake manifolds. Exhaust manifolds collect exhaust and expel it from the engine by connecting to the exhaust pipe. They are usually made from stainless steel or cast iron for strength and heat resistance, but composite materials can also be used to make exhaust manifolds. Ceramic has been a popular choice, though the ceramic can crack under extremely high temperatures.

Exhaust manifolds are comprised of two parts: headers and collectors. The number of headers depends on the number of cylinders in the engine; one header will connect to one cylinder to collect exhaust, so in an 8-cylinder engine, there will be eight headers. The headers connect to a single pipe called a collector, which funnels the exhaust through the exhaust system. Not all cars will have collectors; this is uncommon, except on performance vehicles like race cars or show cars. Exhaust headers help maximize the efficiency of an engine and can help the engine gain added power.

The most common type of manifold failure occurs when heat in any of the manifolds causes cracking. It is not uncommon to hear of cracked manifolds or cracked headers; when this happens the only option for repair is to replace the damaged part, which can be a costly and time-consuming repair.

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Discuss this Article

wizup
Post 3

@Markus - There's a few factors that you'll need to consider before you can determine the life expectancy of your boats manifold system. First, of course it'll depend on the type of boat you have and secondly how you plan to use your boat.

And the third factor is an important one that most people tend to overlook and that is the type of water they plan to put their boat on.

If it's freshwater, such as rivers and lakes, and used mainly for fishing then your probably looking at getting a good fifteen to twenty years out of your manifold. If you're planning some heavy usage in saltwater, then you're looking at only three years, five at the most.

Markus
Post 2

I purchased a used boat here recently, but the seller couldn't give me much information on the mechanics of the boat. She only knew that it was only about four years old and that her late husband would go out on the lake and fish from it every weekend.

Does anyone know what the life expectancy of the exhaust manifold is on a boat?

ladyjane
Post 1

It's really interesting that the article mentions that both the intake and exhaust manifolds are being made of composite materials rather than the typical aluminum and cast iron. This is interesting because over the summer I heard that Ford Motor Company is now supplying new cars with a polyamide plastic intake manifold.

And it gets better, they'll be incorporating recycled polyamide! I love anything that supports a healthy environment so recycling is definitely high on my list of likes!

I was wondering how in the world plastic would hold up to such extreme heat but after some research, I found that Ford ran lots of tests and made several changes until they got the right combination of recycled polyamide plastics.

Ford also found that having the intake manifold made of recycled polyamide materials did not have a negative affect on the performance of the manifold.

Having an intake exhaust made of recycled plastics is not only better for the environment but also makes the car lighter in weight which means better gas mileage. That is a win-win in my book!

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