1. Turbocharging In NA engines the higher the elevation, the lower the engine power, when the vehicle is at 4000m ASL where atmospheric pressure is at 0.6bar, the engine power is about 60% power at sea level. This is also the case in turbocharged BeamNG combustionEngine. The problem is for example if the turbo boost is 1.5 bar, driving in 4000m should give 84% sea level power, since the manifold pressure is 2.1 bar at 4000m and 2.5 bar at sea level. However in BeamNG, 60% power. 2. Engine braking Engine braking is because of the intake vacuum caused by the throttle valve. In current BeamNG calculation, when the engine is fully loaded, actual friction = friction + dynamicFriction * engineAV, and when unloaded, friction + dynamicFriction * engineAV + engineBrakeTorque. The problem is the engineBrakeTorque should * the current atmospheric pressure since the lower the atmospheric pressure, the lower the intake vacuum. This also explained why turbocharged engine is more efficient in high altitudes IRL but less efficient in high altitudes in BeamNG. 3.Engine starting If you use the EngineInfo ui app, you'll see that during engine start, engineBrakeTorque is taken into account. This means the starter motor must overcome engine friction AND engine braking. This is not the case IRL since when engine stopped, there's no intake vacuum and the manifold pressure is equal to the atmospheric pressure
