Throttle Body Sizing Calculator

Enter different throttle body sizes (diameter) to see which will work best with your engine. For better performance at low speeds, choose the smallest throttle which yields a power loss acceptable to you.

Usage Notes

Air Temperature - As measured before entering throttle body. If measurements are not available, typical values are 40-80 °C for a factory airbox/ducting, 20-30 °C for a cold air intake.

Air Pressure - As measured before throttle body. If measurements are not available use atmospheric pressure (101.325 kPa) or appropriate ambient air pressure at your elevation. However, this value will neglect the pressure drop caused by the air filter and airbox/ducting. For boosted engines, add boost pressure to atmospheric air pressure.

Engine Speed - Enter engine speed for peak power, this is the point at which maximum air flow is required.

Volumetric Efficiency - If you don't know the volumetric efficiency, try different values until calculated Power matches your engine.

Throttle Body Bore Diameter - For round bores. For oval bores, an equivalent diameter can be calculated by dividing bore profile perimeter by bore area.

Air Flow Rate - This is the actual airflow rate calculated from the input entered. CFM is calculated for actual pressure drop, this is not directly comparable to manufacturer's flow ratings. Bore diameter is a more reliable way of sizing thr throttle body.

Power - This is the engine power for your current throttle body, see estimated power loss for predicted effects of throttle body changes. If this calculation seems off, make sure you have entered the correct air temperature.

Pressure Drop - This is an indicator of how restrictive the throttle body is. Try to keep this under 2 kPa

Power Loss - Uses SAE pressure correction factor to estimate the amount of power lost due to throttle body restriction. There will always be some amount of power loss, but try to keep this to a minimum.