usually a leaner mix has less power than a richer mix. thus the resistor mod on the IAT sensor (incoming air temp) which tricks it into thinking that more oxygen is coming into the engine and makes you run richer thus giving you more power.
I don't know if they do that same thing on the diesels but ebay is bad about selling you a resistor to give you more power for gas engines.
Or how about selling you a 12Vdc fan and calling it an "Electric supercharger"
Dave252252 
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