I have a 2012 fit and want to install a tanabe medalion exhaust (axle back) with a k & n air filter. Do I have to remap the computer to get increased horsepower...and if I do not remap the ecu I have been told that the computer will adjust to the increased air flow by reducing horsepower? I do not want to reduce hp or fuel economy.

 

All you will have done is increase the noise. No noticeable increase/decrease in HP.

Fit and HP should not be used in the same sentence.