Turbocharger Sizing Calculator

Inputs

Displacement

Total engine displacement.

RPM Min

Lower sizing RPM (spool region).

RPM Max

Upper sizing RPM (flow limit).

Volumetric Efficiency (%)

Typical 80–105% depending on setup.

Boost (gauge)

Gauge boost, not absolute.

Ambient Pressure

Use local barometric pressure.

Ambient Temperature

Affects corrected flow.

Altitude (m)

Optional check for ambient consistency.

Compressor Efficiency (%)

Common range 60–78%.

Intercooler Effectiveness (%)

Higher means cooler manifold air.

Gamma (air)

Use 1.40 near ambient conditions.

Fuel Type

Affects fuel volume estimate.

AFR (optional)

Used only if power target is empty.

Lambda (optional)

Reference only; does not override AFR.

Power Target (hp)

If set, fuel flow uses BSFC.

BSFC (lb/hp-hr)

Typical gasoline turbo: 0.50–0.65.

Reset

Example Scenarios

Scenario	Displacement	RPM Range	VE	Boost	Ambient	Notes
Street 2.0L	2.0 L	2500–6500	92%	14.7 psi	14.7 psi, 25°C	Balanced response and midrange.
Track 3.0L	3.0 L	3500–7500	100%	18.0 psi	14.3 psi, 30°C	Higher flow; watch turbine capacity.
Diesel 2.8L	2.8 L	1600–4200	85%	20.0 psi	14.7 psi, 20°C	Early torque; avoid surge at low flow.

Tip: Run the calculator for 3–5 RPM points to build a sizing curve.

Formulas Used

Pressure Ratio

PR = P_man,abs / P_amb,abs

P_man,abs = P_amb,abs + Boost (gauge).

Compressor Temperature Rise

T₂ = T₁ · (1 + (PR^{((γ−1)/γ)} − 1)/η_c)

T₁ is ambient inlet temperature.

Intercooler Effectiveness

T_man = T₁ + (T₂ − T₁) · (1 − ε)

ε is intercooler effectiveness (0–1).

Air Density

ρ = P / (R · T)

Uses ideal-gas constant R = 287.05 J/(kg·K).

4‑Stroke Volumetric and Mass Flow

V̇ = V_disp · (RPM/2) · VE / 60

ṁ = V̇ · ρ

This tool uses mean RPM between your min and max.

Corrected Mass Flow

ṁ_corr = ṁ · √(T_in/T_ref) / (P_in/P_ref)

Reference: T_ref=288.15 K, P_ref=101.325 kPa.

How to Use This Calculator

Enter displacement, RPM range, and an estimated VE.
Set ambient pressure and temperature for your conditions.
Enter your desired boost and reasonable efficiency values.
Click Calculate, then note PR and corrected airflow.
Compare those points on candidate compressor maps.
Repeat with different RPM points to form a curve.
Export PDF or CSV to share with your builder.

FAQs

1) Why does corrected airflow matter?

Compressor maps are published using corrected flow. Correcting accounts for inlet temperature and pressure so your points compare fairly to the map axes.

2) What volumetric efficiency should I use?

Stock engines often sit around 80–95%. Porting, cams, and tuned intake systems can push VE toward 100% or beyond near peak torque.

3) Is boost the same as manifold pressure?

Boost is gauge pressure above ambient. Manifold absolute pressure equals ambient pressure plus boost. Pressure ratio uses absolute values, not gauge.

4) Why does this use mean RPM instead of every RPM?

It provides a fast sizing point. For real selection, calculate several points across the range and check surge margin, efficiency islands, and choke flow.

5) How accurate is the temperature estimate?

It’s an estimate using efficiency and intercooler effectiveness. Real results vary with heat soak, ducting, compressor speed, and sensor placement.

6) Can I size injectors from the fuel flow result?

It’s a starting point only. Injector sizing also depends on injector count, duty cycle limits, fuel pressure, and safety margin. Validate with logs and targets.

7) What turbine A/R should I pick?

A/R depends on flow, housing options, and response goals. Smaller A/R spools sooner but can raise backpressure at high RPM. Use vendor data when possible.