This Turbo Size Calculator is used in automotive engineering to determine the appropriate turbocharger size for a specific engine.
The correct turbo size is crucial for optimal performance, as an improperly sized turbocharger can lead to poor engine response, reduced efficiency, or even damage to the engine.
How is turbo size measured?
Turbo size is typically measured by the dimensions of its compressor and turbine wheels. The most common measurement is the trim size, which is a ratio of the inducer (inlet) diameter to the exducer (outlet) diameter of the compressor wheel.
This ratio is expressed as a percentage and helps determine the turbo’s flow characteristics.
For example, a turbo with a 60mm exducer diameter and a 52mm inducer diameter would have a trim of:
(52² ÷ 60²) × 100 ≈ 75%Turbo size is often referred to by a simple notation of the compressor and turbine wheel diameters, such as “GT3076R,” where 30 represents the compressor wheel’s exducer diameter in millimeters, and 76 represents the turbine wheel’s exducer diameter.
Turbo Size Calculation Chart
| Engine Displacement (L) | Desired Boost (PSI) | Recommended Turbo Size (Compressor Wheel Diameter mm) |
|---|---|---|
| 1.6 | 10 | 45-50 |
| 2.0 | 12 | 50-55 |
| 2.5 | 15 | 55-60 |
| 3.0 | 18 | 60-65 |
| 3.5 | 20 | 65-70 |
| 4.0 | 22 | 70-75 |
| 4.5 | 25 | 75-80 |
| 5.0 | 28 | 80-85 |
Note: This chart provides general guidelines. Actual turbo sizing depends on various factors including engine design, intended use, and desired performance characteristics.
Turbo Size Calculation Formula
Required Airflow (lbs/min) = (HP × BSFC) ÷ (AFR × VE)Where:
- HP = Target Horsepower
- BSFC = Brake Specific Fuel Consumption (typically 0.5 to 0.6 for turbocharged engines)
- AFR = Air-Fuel Ratio (usually around 11:1 for turbocharged engines)
- VE = Volumetric Efficiency (typically 0.8 to 0.9 for turbocharged engines)
Let’s calculate the required airflow for a target of 400 HP:
Required Airflow = (400 × 0.55) ÷ (11 × 0.85) ≈ 23.53 lbs/min