Is a bigger turbo always more power?

Only if the rest of the system can supply and remove the extra air and fuel. Beyond a point, a larger turbo simply moves the powerband higher and makes the car slower in normal use.

Do I need an external wastegate?

Not always. Internal gates control boost adequately on many setups; external gates are used when the internal gate cannot bleed enough exhaust flow to hold target boost.

Turbo sizing guide for performance builds

Turbo choice is an airflow problem. Match the compressor to the mass of air the engine needs at your target power and the pressure ratio required to move it, and the rest of the decision is about response and duty cycle.

Last reviewed 2026-09-08

Start from airflow, not part numbers

A common planning approximation for a petrol engine is roughly 10 lb/min of airflow per 100 crank horsepower, adjusted for how efficient the combination actually is. That gives a target the compressor map has to cover at a pressure ratio your engine and intercooler can support.

Read the compressor map

Plot your target airflow against the pressure ratio you expect. The point should sit inside the island of good efficiency, away from the surge line at low flow and away from the choke edge at high flow. A turbo running off the map makes heat instead of power.

Response versus top end

A smaller compressor and turbine spool earlier and suit street driving, tight circuits and heavy cars. A larger pair make more peak power but arrive later. Twin-scroll housings, turbine housing A/R and cam timing all move the compromise before you change turbo size.

The supporting hardware moves with the turbo

A bigger turbo changes wastegate control, oil and coolant feed, manifold loading, intercooler duty, exhaust backpressure and fuel demand. Budget the supporting parts at the same time as the turbo.

Common questions

Is a bigger turbo always more power?: Only if the rest of the system can supply and remove the extra air and fuel. Beyond a point, a larger turbo simply moves the powerband higher and makes the car slower in normal use.
Do I need an external wastegate?: Not always. Internal gates control boost adequately on many setups; external gates are used when the internal gate cannot bleed enough exhaust flow to hold target boost.

Parts covered in this guide

Related guides

Plan your own build

Find your vehicle to see compatible parts and staged build targets, or read the other guides.

Specifications shown are planning estimates. Verify compatibility and safe limits with the manufacturer, your tuner or a qualified specialist.