Does seem a big amount from a filter considering I got 3BHP from a custom set up but I guess thats their business so they know their apples!
Although, this temp sensor they played with?? Whats that? Those cheap chips you buy of ebay that claim they give you BHP alter this. It works by fooling your car into running lean.
Its also what mappers do (properly) as they run rich as STD so if he has tweaked that then in effect, he has mapped it to suit the airbox by adjusting the AFR. Why he would do that via the temp sensor though is strange!
Anyway pal, I cant wait to see pics....