Well, no. You don't get something for nothing.
To get more power you have to burn more fuel and air. The point of breathing mods is to allow more air to be crammed in and exhaust gasses let out per piston cycle, meaning more fuel can be burnt, hence more power.
If an engine is not burning all its fuel and your mods improve the efficiency of the burn then that would get you more power for the same fuel, but modern engines use feedback loops to keep the fuel ratio right all the time.
There is some fiddling around the edges of the figures you can argue but basically to get more power you need to burn more fuel.