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What Is an Exhaust Manifold?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 11 March 2014
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    Conjecture Corporation
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An exhaust manifold is a system which is used to vent exhaust gases away from an engine. The manifold extends from the cylinders to the exhaust pipe, collecting and moving exhaust away from the engine. Exhaust can be harmful to inhale, making it very important to have a fully functional exhaust manifold; because it can sometimes be difficult to detect an exhaust leak, people may inhale exhaust gases without being aware of it.

When the pistons in the engine reach the exhaust stroke, they push the exhaust fumes up into the exhaust manifold. The manifold consists of a series of pipes which connect to the cylinders and then consolidate in a central large pipe which vents to the exhaust pipe. A series of gaskets are used to create tight seals so that exhaust cannot escape from the cylinders.

One of the most common problems which can arise with an exhaust manifold is damage to the gasket which acts as a seal. In this case, the manifold needs to be unbolted so that the gasket can be removed and replaced. Another issue which can commonly arise is rust, especially in salty environments. If rust eats through the pipes of the manifold, they can start to leak exhaust fumes into the engine compartment. In a car, these fumes can enter the passenger compartment, making people sick.

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The differing pipe lengths can also lead to an issue known as back pressure, which forces the engine to work harder to push the exhaust fumes out. This can be resolved with an attachment called a header, which uses pipes of the same length to reduce back pressure. Headers are fitted on high performance cars and race cars to increase efficiency. Reducing the amount of work the engine needs to do contributes to higher performance operation, and can make a critical difference with some vehicles.

A mechanic can identify problems with the exhaust manifold if they appear, and make recommendations for repairs or replacement, depending on the nature of the problem. If drivers notice a decline in performance or changes in the way that a car handles, it is a good idea to talk to a mechanic about the issue to see if there is a functional problem with the vehicle which might be causing the change. Paying attention to changes is important for the longevity and performance of the vehicle and for driver health and safety.

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Discuss this Article

Frances2
Post 3

@qwertyq – Good point about the bolts. As an example, if a performance exhaust manifold has been installed on the engine, it’s possible that the type of bolt suggested by the car’s manufacturer won’t work. Obviously, that isn’t a problem if SushiChamp bought their car brand new, but if it’s used, the identity of the manifold is in question. I’m sure there’s a way to tell one manifold apart from another, but they all look the same to me. That’s why I call in the professionals!

qwertyq
Post 2

@SushiChamp – No offense, but I suggest you take your car to a mechanic instead of replacing the bolts yourself. But if you insist, and don’t know what kind of bolts you need, search online for exhaust manifold kits for your car, then buy the exact type of bolt that kit contains. Your car’s user manual might also say what kind of bolt it uses.

You should only do this if you know for certain that your car has the correct manifold on it in the first place. Otherwise, my first recommendation still stands: take it to a mechanic.

SushiChamp
Post 1

I think I need to replace the exhaust manifold bolts in my car, but there are so many types of bolts. How do I choose the right ones?

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