Engine Bay Airflow Calculator
Radiator airflow needed to reject engine heat.
Enter your values
ⓘ Live results
Results
- Estimated heat to radiator
- 229,050 BTU/hr
- Required radiator airflow
- 5,302 CFM
- Note
- Assumes ~30% of fuel energy rejected to coolant at rated power
Quick answer
Radiator airflow is sized from the engine's heat rejection rate and the allowable air-side temperature rise through the core.
CFM = (heat rejection BTU/hr) / (1.08 x dT)
How to use the Engine Bay Airflow Calculator
- 1Enter the engine's rated power output.
- 2Roughly 30% of an internal combustion engine's fuel energy goes to the coolant as heat.
- 3Divide the resulting BTU/hr by 1.08 times the allowable radiator air temperature rise.
Worked example
Using the values the calculator loads with:
Inputs
- Engine power output300 hp
- Allowable air temp rise40 F
Results
- Estimated heat to radiator229,050 BTU/hr
- Required radiator airflow5,302 CFM
- NoteAssumes ~30% of fuel energy rejected to coolant at rated power
Frequently asked questions
Does this account for the fan alone?
It's the total airflow needed through the radiator core, whether from ram air, fan, or both combined.
Turbocharged engines?
Add intercooler airflow separately — this only covers the coolant radiator, not charge air cooling.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.