The guy claims that his little black box richens the mixture. My bet is that it's a plain resistor that goes in series with the temperature sensor. It is supposed to "fool" the computer into thinking that the outside temperature is a little lower, making the air denser. The computer adds more fuel to match the denser air and viola another 200 horsepower, at least.

Zoom,

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Norm in NJ
Next oil change at 230,000miles