Engine Air Flow Calculator

Engine Air Flow Formula:

\[ Q_{cfm} = \frac{RPM \times D}{3456 \times \eta_v} \]

Engine Air Flow (CFM):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is an Engine Air Flow Calculator?

Definition: This calculator estimates the volumetric air flow rate (in cubic feet per minute) that an engine consumes based on its RPM, displacement, and volumetric efficiency.

Purpose: It helps automotive engineers, mechanics, and enthusiasts determine the air requirements for engine tuning, turbocharger sizing, and performance optimization.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ Q_{cfm} = \frac{RPM \times D}{3456 \times \eta_v} \]

Where:

\( Q_{cfm} \) — Air flow rate (cubic feet per minute)
\( RPM \) — Engine revolutions per minute
\( D \) — Engine displacement (cubic inches)
\( \eta_v \) — Volumetric efficiency (dimensionless, typically 0.8-0.9)

Explanation: The formula calculates theoretical air flow based on engine speed and displacement, then adjusts for real-world efficiency.

3. Importance of Air Flow Calculation

Details: Proper air flow estimation is crucial for selecting appropriate carburetors, fuel injectors, turbochargers, and intercoolers, and for optimizing engine performance.

4. Using the Calculator

Tips: Enter the engine RPM, displacement in cubic inches, and volumetric efficiency (default 0.85). All values must be > 0. Volumetric efficiency typically ranges 0.8-0.9 for naturally aspirated engines.

5. Frequently Asked Questions (FAQ)

Q1: What is volumetric efficiency?
A: It's the ratio of actual air volume drawn into cylinders compared to theoretical maximum. Higher values indicate better breathing.

Q2: Why 3456 in the formula?
A: This constant converts cubic inches per minute to cubic feet per minute (1728 in³/ft³ × 2 for 4-stroke cycle).

Q3: How does boost affect this calculation?
A: For forced induction, multiply the result by (boost pressure + 14.7)/14.7 to account for increased air density.

Q4: What's a typical air flow for performance engines?
A: High-performance engines at 6000 RPM might flow 400-600 CFM, while stock engines at 2500 RPM might flow 150-250 CFM.

Q5: How does this relate to fuel requirements?
A: Air flow determines fuel needs - typically 12-15 parts air to 1 part fuel by weight for proper combustion.