Sprint car motors?

I know a lot of sprint cars run small block mopars but I can't figure out how they are getting 800 or 900 hp out of a small block. I will be the first to admit that I do not know a ton about the small block even after rebuilding a few and being on here for 8 years or whatever it is now. But those numbers just seem insane to me.

It's all about air flow and what it takes to make over 2 HP per cubic inch............