yes the engine is getting denser air ...but its the fact that it's cold (not hot) that helps things out. The colder air cools your engine as its taken in. Ping is usually caused by one of 2 things...not enough fuel (lean) or your motor is getting to hot. Thats why guys with turbos run intercoolers...not only to get the denser air...but to get the cooler air to keep internal engine temp down.