Garrett Turbo Size Calculator

Turbo Size Formula:

\[ \text{Turbo Size} = \left( \frac{\text{Engine Displacement} \times \text{RPM}}{3456} \right) \times \frac{\text{VE}}{\text{PR}} \]

Engine Displacement:

liters

RPM:

rpm

Volumetric Efficiency (VE):

decimal

Pressure Ratio (PR):

decimal

Turbo Size:

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1. What is the Turbo Size Calculation?

The Garrett Turbo Size calculation estimates the required compressor flow rate (in cfm) for an engine based on its displacement, operating RPM, volumetric efficiency, and desired pressure ratio. This helps in selecting the appropriate turbocharger for optimal performance.

2. How Does the Calculator Work?

The calculator uses the following formula:

\[ \text{Turbo Size} = \left( \frac{\text{Engine Displacement} \times \text{RPM}}{3456} \right) \times \frac{\text{VE}}{\text{PR}} \]

Where:

Engine Displacement — Total engine displacement in liters
RPM — Maximum engine speed in revolutions per minute
VE — Volumetric efficiency (typically 0.85-0.95 for modern engines)
PR — Pressure ratio (absolute pressure divided by atmospheric pressure)
3456 — Conversion constant for units used

Explanation: The equation calculates the theoretical airflow requirement of the engine and adjusts it for volumetric efficiency and desired boost pressure.

3. Importance of Proper Turbo Sizing

Details: Correct turbo sizing is crucial for achieving desired performance characteristics. An oversized turbo will have lag, while an undersized turbo won't deliver enough power and may overheat.

4. Using the Calculator

Tips: Enter engine displacement in liters, maximum RPM, typical volumetric efficiency (0.85 is a good starting point for street engines), and desired pressure ratio (2.0 = ~14.7 psi boost at sea level).

5. Frequently Asked Questions (FAQ)

Q1: What is volumetric efficiency?
A: VE is the ratio of actual air volume entering cylinders compared to theoretical maximum. Naturally aspirated engines typically have 80-95% VE.

Q2: How do I determine pressure ratio?
A: PR = (boost pressure + atmospheric pressure) / atmospheric pressure. For 14.7 psi boost at sea level: (14.7 + 14.7) / 14.7 = 2.0

Q3: What if my engine has variable valve timing?
A: VVT engines may have higher VE at certain RPM ranges. Use the VE value at your target RPM.

Q4: How does altitude affect turbo sizing?
A: Higher altitudes have lower atmospheric pressure, requiring higher pressure ratios for the same boost level.

Q5: Should I add margin to the calculated size?
A: For performance applications, adding 10-15% margin is common to account for real-world conditions and future upgrades.