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Turbo exhaust housing [Select turbine housing]


Here you get an overview of how the turbo exhaust housing work and how to choose the right one.

This information is to help you understand the differences between the turbine housing, connections and specifications. Have you ever asked yourself, "What is the difference between T3, T4, T6 and V-band turbine housings"? Or maybe "will a T25 inlet flange work on a T3 manifold"? Or, "what does T3/T4 mean?" If so, this information is for you.

  1. Turbine housing
  2. Volute / cm2 - A/R
  3. Twin entry
  4. Singel entry
  5. Turbine outlet
  6. Turbine inlet
  7. Turbine wheel
  8. Turbine housing selection


Turbine housing

Turbine Housing – Collects exhaust gases from an engine and directs them through a spiral / passage that drives the turbine wheel of a turbo and causes it to spin.



Volute - cm2 - A/R

Volute – The passage through which the exhaust gases travel, from the turbine housing inlet to the turbine housing outlet. The passage decreases in area from inlet to outlet, which accelerates the speed of the exhaust gas flow. These aisles / passages are offered in different sizes and are measured in A/R, Area Over Radius or cm2 depending on the manufacturer. The larger the number, the larger the passage / aisle.



Twin entry

Twin Scroll – Turbine housing with double "volute" / cone / inlet. This can improve spool when used with a twin scroll exhaust manifold.



Singel entry

Single / Open Scroll – Turbine casing with a single "volute" / cone / inlet.



Turbin outlet

Where the exhaust gases leave the turbine housing and are led to the exhaust system.


Turbine inlet

Where exhaust gases enter the turbine housing.

Depending on the size and manufacturer of the turbo, there are several types of turbine housing inlets, all with different dimensions. Smaller turbos use smaller inlet flanges, such as T25, while large turbos use larger flanges such as T4 or T6 for example.



Turbine wheel

The turbine wheel is connected to the compressor wheel. Exhaust gases drive around the turbine wheel which in turn spins the compressor wheel which builds up boost pressure. To know how well a turbine housing flows, you also need to know the size and type of turbine wheel that is installed.



Turbine housing selection

Now we have received information about what the different parts mean on a turbine housing, but what gives fast vs. slow spool of the boost pressure? How should you think and how should you know which exhaust housing to choose for your effect?

Turbine size is discussed in:

High flow = High power = Slow spool
Larger turbine wheels give more flow than correspondingly smaller ones as there is more room for exhaust gases at higher revolutions where the power comes from.

Low flow = Low power = Fast spool
Smaller turbine wheels give better spool than correspondingly larger ones as there is less space for the exhaust gases and the turbo is forced to spin up faster at low revs.

The larger turbine wheel may have more blades that take up more space and may impede the flow more than a smaller turbine wheel with fewer blades. In other words, a larger turbine wheel with more blades can flow worse than a smaller one with fewer blades.

The size of the turbine wheel is measured on the inducer and exducer



Turbine housing

Click below to see different exhaust housings

Garrett BW SX-E BW EFR