Turbine Housings

The turbine housing collects exhaust from the manifold and directs it onto the turbine wheel through a spiral passage called the volute. How tightly that passage narrows, expressed as the A/R ratio, determines how fast exhaust hits the wheel. That's why the turbine housing has such a strong effect on spool, drive pressure, exhaust gas temperature, and how much the turbo can flow at high rpm.

How does turbine housing A/R affect performance?

A smaller A/R typically speeds up exhaust flow onto the wheel, so the turbo spools sooner and responds faster. It commonly raises drive pressure and EGT and can limit power at high rpm.

A larger A/R typically lowers drive pressure and supports more top-end flow, but the turbo spools later.

The right A/R depends on engine size, power goal, rpm range, and how the vehicle is used. Towing and daily driving commonly favor response, while high-rpm builds commonly favor flow. Your tuner can help confirm the best choice.

• Match your turbo and turbine wheel. The housing must fit your turbo brand, frame, and turbine wheel size and contour. Check the data plate and current housing.
• Match the inlet flange. Confirm the flange type, such as T3, T4, T6, or V-band, and whether the manifold is divided or undivided.
• Choose divided or undivided. Divided (twin-scroll) housings pair with divided manifolds and commonly improve spool by keeping exhaust pulses separated. Undivided housings are simpler and common on single-scroll setups.
• Choose the wastegate setup. Internally wastegated housings use a built-in flapper and actuator. Open housings require an external wastegate. Make sure the housing matches your boost control plan.
• Consider material. Cast iron housings suit most applications. Higher-alloy or stainless housings are commonly chosen for high EGT and heavy-duty use.
• Check the outlet. Confirm the outlet flange matches your downpipe or plan for an adapter.