I had similar concerns so I dynoed hood down. I have a custom full airbox and 9" K&N. The K&N, airbox, and 75mm MAF made 12 HP more than stock SVT parts (again hood down) though I did not acess the indivdual contributions (hard to do as MAF meter was calibrated specifically to the K&N.)
But without an airbox I agree, stock probably better on a hot day..I have underhood temp recordings to back this up and I actually had reverted to stock airbox from KKM in the summer due to heatsoak. airbox eliminated heatsoak.
