A system for estimating a scavenging ratio of an engine of a vehicle, the scavenging ratio relating to an overlap of opening of intake and exhaust valves (144, 148) of a cylinder of the engine, the system comprising: an intake manifold absolute pressure sensor configured to measure a pressure of air in an intake manifold of the engine; an engine speed sensor configured to measure a speed of the engine; and a controller of the engine, the controller being configured to: retrieve, from a memory of the controller a model surface relating various measurements of the engine speed sensor and valve overlap durations to modeled scavenging ratios of the engine; generate, based on calibration data measured by a calibration system, a calibrated multiplier surface relating various measurements of the intake manifold absolute pressure and engine speed sensors (140, 124) to calibrated multipliers; determine a modeled scavenging ratio of the engine based on the measured engine speed and a known overlap duration using the model surface; determine a scavenging ratio multiplier based on the measured intake manifold absolute pressure and measured engine speed using the calibrated multiplier surface; determine the scavenging ratio of the engine by multiplying the modeled scavenging ratio by the scavenging ratio multiplier; and control the engine based on the determined scavenging ratio. an intake manifold absolute pressure sensor configured to measure a pressure of air in an intake manifold of the engine; an engine speed sensor configured to measure a speed of the engine; and a controller of the engine, the controller being configured to: retrieve, from a memory of the controller a model surface relating various measurements of the engine speed sensor and valve overlap durations to modeled scavenging ratios of the engine; generate, based on calibration data measured by a calibration system, a calibrated multiplier surface relating various measurements of the intake manifold absolute pressure and engine speed sensors (140, 124) to calibrated multipliers; determine a modeled scavenging ratio of the engine based on the measured engine speed and a known overlap duration using the model surface; determine a scavenging ratio multiplier based on the measured intake manifold absolute pressure and measured engine speed using the calibrated multiplier surface; determine the scavenging ratio of the engine by multiplying the modeled scavenging ratio by the scavenging ratio multiplier; and control the engine based on the determined scavenging ratio. retrieve, from a memory of the controller a model surface relating various measurements of the engine speed sensor and valve overlap durations to modeled scavenging ratios of the engine; generate, based on calibration data measured by a calibration system, a calibrated multiplier surface relating various measurements of the intake manifold absolute pressure and engine speed sensors (140, 124) to calibrated multipliers; determine a modeled scavenging ratio of the engine based on the measured engine speed and a known overlap duration using the model surface; determine a scavenging ratio multiplier based on the measured intake manifold absolute pressure and measured engine speed using the calibrated multiplier surface; determine the scavenging ratio of the engine by multiplying the modeled scavenging ratio by the scavenging ratio multiplier; and control the engine based on the determined scavenging ratio.