HP ↔ CFM Calculator (Horsepower to Airflow)

Q: What does “CFM per HP” mean?

It’s a rough ratio linking airflow to power. Using 1.30 CFM per HP as a baseline, horsepower can be estimated as CFM ÷ 1.30, and required airflow can be estimated as HP × 1.30.

Q: Is 1.30 CFM/HP always correct?

No. It’s a starting point for naturally aspirated gasoline engines. Real results depend on volumetric efficiency, cylinder head efficiency, cam timing, rpm range, fuel, and boost.

Q: Should I use this to choose a carburetor size?

Use it as a quick check, but carb sizing is usually better estimated with a CID/RPM/VE-based calculator. Then compare your result with common carb sizes.

Q: What if I’m running boost?

Boost changes the airflow-to-power relationship. This tool can still help as a sanity check, but boosted combos should be planned with more detailed airflow and fuel system considerations.

Use this Fastime Performance calculator to estimate the relationship between airflow (CFM) and horsepower (HP) using a simple rule-of-thumb. It’s a quick way to sanity-check a combo when you’re choosing a carburetor, comparing head/port airflow, or sizing an intake/throttle body for an EFI setup.

What this tool is good for

Estimating airflow needed to support a target horsepower.
Estimating horsepower potential from a known airflow number.
Getting a quick “does this make sense?” check before spending money.

Use it with these Fastime tools

Carb CFM Calculator (CID/RPM/VE-based sizing)
All Calculators & Tools (full toolbox)

Quick note: This is a rule-of-thumb. Real airflow/HP depends on VE, fuel, boost, rpm range, cam timing, head efficiency, and the whole combo. Use this as a starting point—then validate with real parts data and goals.

Popular parts related to airflow

Fastime Performance HP ↔ CFM Calculator

Simple rule-of-thumb relationship between airflow (CFM) and horsepower. Use CFM ≈ HP × (CFM/HP).

Approximate Result

Required Airflow 520 CFM Using CFM ≈ HP × (CFM/HP)

Uses CFM ≈ HP × (CFM/HP). Default 1.30 CFM/HP is a common NA rule of thumb.
Real results depend on VE, boost, fuel, rpm range, and the whole combo—treat this as a guideline, not a dyno sheet.

FAQ: HP vs CFM

What does “CFM per HP” mean?

It’s a rough ratio that links airflow to power. If you assume 1.30 CFM per HP, then a 520 CFM airflow estimate would be roughly 520 ÷ 1.30 ≈ 400 HP.

Is 1.30 CFM/HP always correct?

No—think “starting point.” Cylinder head efficiency, rpm range, cam timing, VE, and boost can move the real number. Use this calculator to get in the ballpark, then validate with your parts and goals.

Should I use this to choose a carburetor size?

Use this as a quick check, but for carb sizing you’ll usually get better direction from the Carb CFM Calculator (it uses CID, rpm, and VE). Then compare options in the carburetor category.

What if I’m running boost?

Boost changes the airflow/power relationship significantly. This tool can still provide a “sanity check,” but boosted combos should be sized using more detailed airflow and fuel system planning.

Want the full toolbox? Visit Fastime Performance Calculators & Tools.