I am assuming this is a 350, right? And are you doing a complete rebuild on this engine? It is hard to estimate how much hp gain you will get--maybe 5 or so with the electric fan, the Air-Gap and Demon in good tune could be around 20. Vortec heads would add more but headers and a free flowing exhaust could add up to 15 per cent more. Combined with a good street cam like a CompCams Magnum 270 or an XE268, you could have around 350 hp when it is all said and done. Why do you want to use a Demon carb? Personally, I think they are over-rated, and you really have to know what you are doing to tune them.