Turbine Housings

Is your turbo too slow to respond, or does backpressure get too high at high revs? The turbine housing controls how the exhaust gas hits the turbine wheel. Here you choose a housing by A/R ratio, flange and wheel size – for those upgrading or rebuilding a turbo in their project.

What the turbine housing does

The turbine housing guides the exhaust gas from the exhaust manifold onto the turbine wheel. The housing's A/R ratio – the relationship between the passage cross-section and the distance to the wheel's centre – affects when the turbo builds boost and how much backpressure the engine faces at high revs. A smaller A/R typically gives quicker response, while a larger A/R typically lowers backpressure at the top end. The right choice depends on engine, turbo and use.

How to choose a turbine housing

Look at several factors at once – a larger A/R is not automatically better:

• Turbine wheel: the housing must match your wheel's diameter, e.g. the BorgWarner housings in the S400SX series are specified for 87 mm.
• Flange: T4, T6 and other flanges must match the manifold, e.g. the Forced Performance HD5598 housing has a T6 flange.
• Single or twin scroll: twin scroll keeps the exhaust pulses separated and requires a manifold built for it; BorgWarner's EFR B2 housing, for example, is a twin scroll housing with wastegate.
• Wastegate: check whether the housing has an integrated wastegate or whether your setup uses an external one.
• Material: e.g. the TiALSport housing for GT35XX in stainless steel.

Installation and maintenance

The housing mounts to the centre housing, and you'll find matching CHRA units and compressor housings in the sister categories. Use new gaskets and follow the manufacturer's instructions for tightening bolts and V-band clamps. Cracks at the flange or wastegate port can be caused by heat stress and should be inspected. Brands in the category also include Garrett and Turbosmart. Whether the modification affects inspection and road approval depends on the product and the car, so check this for the specific part number.

Frequently asked questions

Which A/R ratio should I choose for my turbine housing?

It depends on displacement, turbo size, power target and rev range. A smaller A/R typically gives quicker boost build-up, a larger one typically less backpressure at the top end. It's a good idea to start from the turbo manufacturer's recommendation for your specific turbo.

Can I change the turbine housing without changing the turbine wheel?

Yes, if the new housing is made for your wheel's exact diameter and type. The housing must also fit the centre housing and the exhaust manifold flange, so check the specification for the specific part number before ordering.

Does the engine management need adjusting after a new turbine housing?

Often, yes. A new A/R ratio can change when and how quickly boost builds and how the wastegate regulates it. Have the tune checked so that boost, air-fuel ratio and exhaust gas temperature stay within safe limits.