It has something to do with either modifying the signal of the air temperature or head temp sensor. They are usually a "volume" control that regulates olhms passing through a wire. The "volume" **** is the adjuster. It will richen or lean your fuel mixture. Possibly adding 5-10 horsepower to a well modified n/a engine. No way could it add 20hp unless you are running a turbo charged engine and your computer is not working right to give you the proper fuel mixture. Its a 2-dollar Radio Shack item, and basically a scam. You can make one yourself if you are curious.

I heard of someone doing that to the head temp sensor on an n/a 280zx, and it sorta worked. Maybe added a couple pounds of torque. Just barely enough to notice. It also decreases your milage when activated.