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Holley Carb CFM Formula:
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The Holley Carb CFM formula calculates the optimal carburetor size (in cubic feet per minute) for an engine based on its maximum RPM, displacement, and volumetric efficiency. This ensures proper air/fuel mixture for optimal engine performance.
The calculator uses the Holley CFM formula:
Where:
Explanation: The formula calculates the volume of air the engine can theoretically consume at maximum RPM, adjusted by its volumetric efficiency.
Details: Correct carburetor sizing is crucial for engine performance. An oversized carb can cause poor low-end torque and throttle response, while an undersized carb restricts high-RPM power.
Tips: Enter maximum expected RPM, engine displacement in cubic inches, and volumetric efficiency (use 0.85 for street engines, up to 1.2 for highly modified race engines).
Q1: What's a typical VE value for street engines?
A: Most street engines have VE around 0.80-0.90. High-performance engines may reach 0.95-1.0, and race engines with optimized airflow can exceed 1.0.
Q2: Should I round up to the nearest available carb size?
A: Generally yes, but stay within 10% of calculated CFM unless building a dedicated race engine.
Q3: How does altitude affect carb sizing?
A: At higher altitudes, air density decreases. You may need slightly larger CFM to compensate for thinner air.
Q4: What about forced induction engines?
A: This calculator is for naturally aspirated engines. For turbo/supercharged engines, use different calculations that account for boost pressure.
Q5: How important is carb size vs. tuning?
A: Proper tuning can compensate for slight sizing variations, but correct CFM is fundamental to optimal performance.