Belly Pan / Skid plates on turbo and non-turbo engines will pull cooling air to the fire wall rather than dumping air to the road after passing the radiator. The cooling effect with a a belly pan will tend to pull more air through the inlet. I cannot quantitatively measure this, my opion is based on observation of turboprop aircraft. As engine cowl inlet size decreased (cross sectional area of the engine cowl remaining the same) there was an increase in speed and a decrease in fuel consumption. Pitot cowling also increased internal engine compartment pressure (ram air). Please be aware all air flow is a trade off with travel speed being the largest variable. '87 240, 01 V70 2.4T