How to Calculate Turbo CFM


A turbo compressor flow map is generally measured in cubic feet per minute, or cfm. The cfm of airflow is affected by various engine and atmospheric parameters. Many variables, such as the turbo system piping volume and ambient temperature, slightly modify the exact compressor flow map of your turbo system. However, by using approximate values for your engine's volumetric efficiency and pressure ratio, you can find out the ariflow of your turbo system in cfm with a relatively simple calculation. This cfm calculation can help you decide on an efficient boost pressure setting for your turbo system.

Things You'll Need

  • Calculator
  • Engine specifications
  • Multiply the engine displacement, in liters, by any given RPM value. Use your engine's RPM value at redline for a starting point, then plug different RPM values into the calculation later to determine the airflow in cfm of your turbo system across the entire rev range.

  • Multiply the product of the multiplication in Step 1 by 90. This is an estimated volumetric efficiency percentage for production four-stroke engines. Many specific attributes of the engine and turbo system slightly affect the exact volumetric efficiency value. However, using the estimated volumetric efficiency of 90% will give you an accurate cfm calculation for tuning purposes.

  • Add the value of the intended boost pressure of your turbocharger at the given RPM to 14.7. Then, divide this sum by 14.7. This gives you an estimated value for your turbo system's pressure ratio. Pressure ratio is affected by a number of turbocharger attributes, as well as various atmospheric conditions. However, this estimated pressure ratio value will allow you to easily calculate the cfm for tuning purposes.

  • Multiply the pressure ratio value calculated in Step 3 by the product of the multiplication performed in Step 2. Then divide the product of this multiplication by 5,660. The quotient of this final division is the airflow in cfm for your vehicle at the chosen RPM and boost pressure level.

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