Throttle Body Size Calculator

The throttle body is the valve that controls airflow into your engine — size it too small and you choke power, too large and you lose throttle response. Enter your engine displacement, target horsepower, maximum RPM, and number of throttle bodies into the Throttle Body Size Calculator to get the recommended throttle body diameter in mm or inches. Secondary outputs include total flow area, air velocity at max power, and CFM requirement.

CID

Engine displacement in cubic inches

HP

Desired engine horsepower output

RPM

Peak operating RPM

ft/sec

Maximum recommended air velocity (typically 300 ft/sec)

Results

Recommended Throttle Body Diameter

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Diameter (Inches)

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Total Flow Area

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Air Velocity at Max Power

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CFM Requirement

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Frequently Asked Questions

What is the optimal throttle body size for my engine?

The optimal throttle body size depends on your engine's displacement, target horsepower, and maximum RPM. Generally, you want to maintain air velocity between 250-300 ft/sec at peak power for best throttle response and power delivery.

Can a throttle body be too big for my engine?

Yes, an oversized throttle body can hurt performance by reducing air velocity at low RPMs, leading to poor throttle response and reduced torque. The goal is to size it appropriately for your power goals.

How does the number of throttle bodies affect sizing?

With multiple throttle bodies (like individual runner systems), each throttle can be smaller since the total airflow is divided among them. This often provides better throttle response than a single large throttle body.

What's the difference between single and dual throttle body setups?

A single throttle body is simpler and more cost-effective, while dual throttle bodies can provide better airflow distribution and higher flow capacity for high-performance applications.

Should I consider throttle body sizing for turbo engines differently?

Yes, turbocharged engines have different airflow characteristics due to forced induction. The throttle body sizing should account for the increased air density and pressure ratios from the turbocharger.

What air velocity should I target for best performance?

Most experts recommend keeping air velocity at or below 300 ft/sec at maximum power. Velocities between 250-300 ft/sec typically provide the best balance of power and throttle response.

How accurate is throttle body size calculation?

These calculations provide a good starting point, but actual results may vary based on intake manifold design, cam timing, and other engine modifications. Always verify with dyno testing when possible.

Do I need to consider intake manifold design when sizing throttle bodies?

Absolutely. The intake manifold design, runner length, and plenum volume all affect airflow dynamics and should be considered alongside throttle body sizing for optimal performance.