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Exhaust System: Parts and Assembly

With this information, you will know what is included in an exhaust system and how the parts are connected. Whether it's for an original car, a tuned car or a racing car. Speeding has been building and assisting with exhaust systems for both street cars and winning race cars for over 10 years with very good results and now it's your turn to learn how to do it the best way.

We will walk you through all the parts so that you feel safe with your choices and how to connect these and make them work together in the best way.

Overall, it can be said that an exhaust system directs exhaust gases from the engine away from the car chassi. On the way, a catalytic converter cleans the exhaust gases and silencers keep the noise level down.

The various parts of the exhaust system:

  1. Exhaust manifold / Headers
  2. Turbocharger
  3. Downpipe (Front exhaust pipe)
  4. Flex pipe
  5. Catalytic converter
  6. Silencer
  7. Exhaust flanges / V-band
  8. Pipes / Tubing
  9. Cellfix
  10. Lambda sensor
  11. Assembly details
  12. Exhaust wrap/ Heat protection
  13. Back pressure

When you read about different exhaust parts below, you will feel confident with the choice of parts and you can overlook problems. In this way, you get a better and cheaper exhaust system without having to guess.



Exhaust manifold / Headers

An exhaust manifold collects the exhaust gases from all cylinders down to an exhaust pipe or to the turbo. If it is a V engine, two exhaust pipes can be used all the way, one for each cylinder bank.

Original exhaust manifolds are cast and very compact with sharp angles. This is cost-effective and service-friendly but not so good from a power point of view. If the car is to be tuned, you often want a different design on the manifold without sharp angles. This is where original and aftermarket manifold differ.

It's called xtractor manifolds when all the pipes are the same length and have soft long radius bends. This takes up a lot of space in the engine compartment but allows high exhaust gas flow. This type of manifold is used for engine tuning / performance engines.




The turbo is part of the exhaust system, more precisely the turbine and turbine housing connections (turbine housing) where the exhaust gases pass. Original, even the turbine housing can fit the manifold as a single part. In the aftermarket, these are bolted together as separate parts.

The power a turbine housing / exhaust housing can handle is determined by how much exhaust gases pass through and how much space is left for the exhaust gases. If there are more exhaust gases than there is room, the exhaust housing will act as a restriction on high revs when there is a high exhaust gas flow.



Downpipe (Front exhaust pipe)

The front exhaust pipe that is mounted directly after the turbo or manifold and this is called downpipe. A catalyst, flex pipe and lambda probe are also usually mounted / included in this pipe. This part can have a larger diameter than the rest of the exhaust system as the exhaust gases are hottest near the engine and hot exhaust gases take up more space than cold ones. To get a good flow and more power / less back pressure, the downpipe can have a larger diameter for better flow. Further down the exhaust system, the exhaust gases cool down and the diameter of the exhaust pipe can narrow.



Flex pipe

Flex pipe is fitted to compensate for movements. Therefore, this can also be called a compensator in certain contexts. The downpipe is mounted on the turbo / manifold at one end. The other end is mounted against the engine and then comes the flex pipe and connects to the rest of the exhaust system. In this way, the downpipe is fixed against the engine and the movements that occur between engine and body / the rest of the exhaust system (catback) are taken up by the flex pipe.

The two most common types of flex pipe are a pleated bellows and a metal spiral.

The pleated bellows is not smooth on the inside like the steel spiral, but instead withstands greater forces, which makes it the choice in the aftermarket. So even if the steel spiral with its smooth inside has better flow, the pleated bellows is used in performance exhaust systems. Both can absorb movements equally well and both are reinforced with an outer steel braid that holds the construction together.

A flex tube, regardless of model, must be mounted so that they are unaffected in the rest position. There should therefore be no applied forces when the car is stationary. If the flex pipe is already bent in the resting position, it will quickly break when more movements takes place when driving.



Catalytic converter

A catalyst has the task of cleaning the engine's exhaust gases (catalytic exhaust gas purification). In order for the catalyst to work, the temperature needs to reach at least 5-600 degrees. Therefore, a catalytic converter should not be placed too far from the engine.

There are several different types of catalysts where both external design and content differ.

Original, the catalytic converter is attached to the rest of the exhaust system. In the aftermarket, this often comes with clamps so it can easily be dismantled for inspection as this is a service part. An aftermarket catalytic converter has weld connections or connections that can be clamped onto an existing pipe using clamps.

The content is metallic or ceramic, of which the metallic is most common in the performance aftermarket. The content is also measured in density or cells per inch, where the most common are 100, 200 and 300 cells per inch. More cells per inch give better exhaust gas cleaning but poorer flow. Therefore, a 100 cell catalyst has the best flow but do not cleas as good as the other types. However, a catalytic converter with 100 cells per inch can pass an MOT / inspection without problems if the rest of the engine's hardware and software is in order.

More holes (300 cell) give better cleaning but poorer flow and more back pressure.
Fewer holes (100 cell) give poorer cleaning but better flow and less back pressure, which is common in cars with more power.

Difference between racing catalyst and sports catalyst?
The difference between the two above is the number of cells. 100cell is usually called a race catalyst, but how you then categorize the rest is individual. The easiest way is to talk cells per inch, so there are no misunderstandings.

Race Catalyst = 100 cell
Sports catalyst = 200 or 300 cell

What size catalytic converter?
What size catalyst is needed has to do with size of connections and flow through the catalyst core itself. It is not easy to know which one to have without seeing what has worked for others or trying it out. It will usually create back pressure in the exhaust system which results in more heat.

Just like the turbo's exhaust, it is impossible to say how much power a certain catalyst can handle. This depends entirely on several different factors. Here we list just a few that only have to do with the exhaust system:

  • How much exhaust gas must pass (including engine volume, supercharging and rpm)
  • How many cells per inch
  • Catalyst diameter and length.
  • The exhaust system's other diameter, length, number of bends and type of bends.

Catalytic converter Quick facts:

100cell = Less cells = More flow = Can handle bigger engine displacement = Can handle more power = Decreased exhaust emission control =  Not blocked as easily = Less back pressure = Less sound dampening

200cell = More cells = Less flow = Can handle smaller engine displacement = Can handle less power = Increased exhaust emission control = Blocked easier = More back pressure = More sound dampening

Bigger diameter = Bigger body = More flow = Used with bigger engine displacement = Takes up more space = Less back pressure

Smaller diameter = Smaller body = Less flow = Used with smaller engine displacement = Takes up less space = More back pressure

A clogged catalytic converter can create major problems as back pressure and heat build up.
Two parallel catalytic converters can be used to increase flow / engine power.




Silencers dampen sound and resonance and are available in different variants both in terms of appearance and assembly as well as content.

There are many variants but all always have at least one inlet and one outlet. These are mounted with clamps or by welding to the rest of the exhaust system.

Since the pipe that leads the exhaust gases through the muffler is perforated (has holes in it), the sound can pass out into the muffler itself and dampen the sound.

What causes the sound to be dampened in a muffler:

  • Shape of the muffler body
    If the body of the muffler is large, sound is dampened better than a small muffler. This is so that there is room for more damping. Even the shape of the muffler can reduce the sound level. A large muffler body allows for better noise reduction even though it is of the full flow type.
  • Damper wool
    This is something that reduces the sound and there are many theories about how a silencer should be wound. Hard or loose, type of cushion / wool and whether it should be sectioned into compartments with and without wool alternately. This does not affect engine power.
  • Number and size of the holes in the perforated pipe.
    The number of holes and the size of the holes in the perforated tube barely affect engine power, but the noise level all the more. In this way, you can have a full flow muffler with good damping without power loss.
  • Full-flow or not
    A full flow muffler has a straight perforated tube that allows the highest flow through the muffler, this also means less noise reduction than the classic oem muffler where the exhaust must pass diagonally / zigzag through the muffler, which also captures / dampen most of the sound.


How much power a muffler can handle depends on the inner diameter and whether it is a full flow muffler or not.
If you want as much damping as possible, a muffler as large as possible should be chosen.



Exhaust flanges / V-band

An exhaust system is often very long and needs to be split at at least one point in order to be handled. Therefore exhaust joints or exhaust flanges are used. These are steel plates that are welded to the exhaust pipes and bolted together with a gasket between them.

Now V-bands are used more and more. These are two round steel flanges that are clamped together using a clamp that resembles a hose clamp with edges. The Hurricane V-band clamps have a built in conical seal.



Pipes / Tubing

The entire exhaust system is made up of pipe parts and other accessories such as catalyst, exhaust flanges, silencers, flex pipes and more. The original pipe parts are bent in machines to fit the car's shape perfectly. In the aftermarket, these parts are available pre-bent in 30, 45, 60, 90 and 180 degrees and are assembled together like Lego with exhaust clamps or welding.

Different materials for pipe parts are available, but also different dimensions depending on where in the exhaust system the parts are to be used. This is so that you, the builder, can get an exhaust system according to your wishes.




Cellfix lambda delete is an adapter that inhibits exhaust gas flow to the lambda probe. This adapter sits between the exhaust pipe and the lambda sensor, which inhibits the exhaust gas flow.

The Cellfix lambda delete adapter is used when, for example, you have installed racing catalysts on a newer car and receive error codes on the exhaust gas treatment. When this adapter is mounted into the lambda outlet between the exhaust system and the lambda probe, the error code due to too high a flow will disappear. There is a standard M18x1.5 thread on the cell fix, so they fit all commonly used lambda sockets.

Cellfix areas of use:

  • Solution to error code P0420 with race / sports catalyst
  • Relocation of the lambda probe, which is located directly after the turbo
  • Adapt the lambda probe out a bit at extreme exhaust gas temperature


Lambda sensor

A lambda probe measures the air-fuel mixture in the exhaust system so that the car's engine management (ECU) knows how much fuel to inject. A lambda sensor sits in front of the catalytic converter and helps the ECU with the fuel mixture (control probe). The second lambda probe is behind the catalytic converter and tells about the function (diagnostic probe).

In the aftermarket / performance, only one control probe is used in front of the catalyst as service intervals are frequent and the catalyst is visually inspected. Back pressure in the manifold / after the turbo can also be measured and then tells if a catalytic converter is becoming clogged.



Assembly details

In addition to exhaust pipes and the various parts of the exhaust system, which each have a specific function, there are accessories and mounting parts in an exhaust system. Hooks are mounted in the car body and on the exhaust system. With the hooks, the exhaust system can be hung with the help of the exhaust mounting rubbers. These allow some mobility in the system so that it is not mounted stiff to the car chassis. This is to prevent cracks from occurring when the body and exhaust system want to move. The exhaust rubber thus acts as a link between the hook on the exhaust pipe and the hook on the exhaust system.

Original mounting points in the body are often very good and can be used as inspiration for new construction.

Performance exhaust rubber is available which further holds the exhaust system in place.



Exhaust wrap/ Heat protection

Exhaust wrap, turbo hat and heat protection mat are some parts used to keep the temperature of the exhaust system down. Above all, it is the part of the exhaust system that is in the engine compartment that you want to have heat shielded. This is because that the engine itself emits heat and you do not want to add more radiant heat into the engine compartment caused from the exhaust system.



Back pressure

In a turbo engine, there is more or less back pressure in the exhaust system. This back pressure prevents the turbine from spinning freely and thus slows down the turbo spool. Back pressure will exist in an exhaust system but the important thing is to keep this as low as possible on a turbocharged engine.

Back pressure at idle / low RPM largely affects how well a turbo spools up. Therefore, it is a trade-off how big an exhaust system you want.

  • Smaller diameter exhaust pipes sound less but give more back pressure
  • Larger diameter exhaust pipes make more noise but give less back pressure

To reduce the back pressure in the exhaust system, avoid tight bends (short radius bends) in the exhaust system. Even recirculation of the wastegate in the exhaust system affects flow / turbulence and there with the back pressure.

The sound is also affected by various factors such as the number and size of silencers.