The air density difference in 20 degrees Celsius is less than 10%, for exact numbers google it or look at this chart
http://docs.engineeringtoolbox.com/d...nsity_SI_2.png
Good job though. What was the change at 100km/h?
As always the incoming colder days are mileage killers, on my test car I already have a full upper and 85% lower grill block and it`s still too cold for the engine with air temps being a little over 0°C. But let`s keep our heads up.