Intake CFM Calculator
Compute engine airflow (CFM) requirement from displacement, RPM, and volumetric efficiency — and get carb/throttle body sizing.
How to Use
- Enter displacement, peak RPM, and VE (85% stock, 100% well-built NA, 110-130% turbo).
- Result gives ideal CFM and carb / throttle-body recommendation.
Engine
Airflow
Formulas
Theoretical CFM
CFM = (CID · RPM · VE/100) / 3456
Carburetor
CFM_carb ≈ 1.25 · CFM
Throttle body (mm)
D_tb ≈ √(CFM · 0.45)
Mass flow
ṁ (lb/min) ≈ CFM · 0.0765
Frequently Asked Questions
Why "add 25%" for a wet-flow carb?
Carbs are rated at 1.5" Hg — higher restriction than a TB. Rule of thumb: carb CFM ≈ 1.25× theoretical to avoid bog at WOT.
Which VE should I use?
Stock: 80-85%. Good heads + cam: 95-100%. Turbo at WOT: 110-140%.
Common Use Cases
Carb sizing
Avoid the classic "too big" Holley that never transitions properly.
Throttle body pick
Get peak HP without wasting spool on a TB that is too big.
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