FREE TOOL · TURBO SIZING
Boost pressure converter + PR
Convert turbo boost between bar / psi / kPa (gauge and absolute) and compute the compressor pressure ratio at any altitude. Essential for turbo selection: a PR > 3.0 needs intercooling on petrol; a PR > 4.0 needs a billet wheel.
What PR really means
Compressor Pressure Ratio = absolute outlet pressure / absolute inlet pressure. PR=1 means no boost. PR=2 means double atmospheric pressure. Turbo maps (compressor maps) are plotted against PR and airflow — picking a turbo requires matching the operating PR + airflow to the compressor's efficiency island.
| PR | Typical use | Concerns |
|---|---|---|
| 1.5-1.8 | Stage 1 petrol turbo (e.g. 1.0 bar) | None — well inside any modern compressor |
| 2.0-2.5 | Stage 2-3 petrol turbo | Intercooler upgrade recommended |
| 2.5-3.5 | Big single petrol setup | Need air-to-water IC, methanol injection, or both |
| 3.5+ | Drag / time-attack only | Billet wheel required, IAT cooling critical |