How would you estimate the charge density (air actually entering the cylinder) in an ICE? Assume the outside is standard pressure and temperature of 15*C (60* F) and 101.3kPa (14.7psi). At high airflow speeds (Wide Open Throttle), pressure in the manifold should approximate atmospheric conditions. There is also less time for heat soak while the air travels to the cylinder. What about a lower throttle (air speeds)? Assume the manifold pressure is 50kPa, but we keep the temperature constant. Is the density really half of the atmospheric conditions (using 2.7 * P / T ; P in psi and T in *R)?