Start with the use case
A daily-driven street car usually benefits from a responsive turbo that reaches useful boost early and does not require constant high RPM. A drag car may accept more lag if the setup leaves the line in boost. A circuit car needs predictable transient response and heat management. A dyno build may chase a number that would be frustrating on the road.
Compressor size and airflow
The compressor must flow enough air for the power target without operating in an inefficient zone. Too small and it becomes a heat pump. Too large and it may be lazy below the RPM range where the car is actually used. A sensible turbo often feels faster because it makes torque in the real driving window.
Turbine housing matters
A smaller turbine housing can spool quickly but increase exhaust backpressure at high flow. A larger housing can breathe better up top but may slow response. The best choice balances turbine flow with the engine’s displacement and intended boost range.
Leave headroom but avoid fantasy sizing
Some headroom is good. Too much headroom can make the car worse. Choose for the power level you genuinely intend to use, not the number you might chase years later.