Some standalone-ECU calibrations use throttle position and engine speed as the primary axes of the main volumetric-efficiency table instead of manifold pressure and engine speed. This can resemble traditional Alpha-N, but the underlying strategy is different.
Why use throttle position?
Modern model-based ECUs already account for manifold pressure when calculating cylinder air mass and required fuel. Using manifold pressure again as a primary VE-table axis can duplicate information already present in the fuel model.
Throttle position provides another useful description of engine airflow. On suitable combinations, throttle position and RPM can produce a more useful calibration surface and more consistent drivability.
This can be helpful with individual throttle bodies, large camshafts, unstable manifold vacuum, turbocharged engines with complex airflow behavior, and applications where MAP alone does not adequately represent load.
This is not traditional Alpha-N
Traditional Alpha-N calculates fuel primarily from throttle position and RPM and may not adequately account for manifold pressure, displacement, injector characteristics and other modeled variables.
A modern throttle-indexed VE table can still operate inside a complete model that considers pressure, temperature, displacement, injector data and fuel properties. The correct load strategy depends on the ECU, engine, sensors, induction system and intended use.
Do not change load-axis configuration without a matching calibration.
