i'm going to be getting a 99 STi RA soon, and i have a question about mods.

so far the car will have-

parallel fuel rails
flipped alternator
MPH converter with delimiter
all hoses changed to silicone
light weight pulleys

was wondering if i should tune if i install a bellmouth downpipe that exits at 2.5 inch to match the stock piping

 

You do not have to get the car checked/mapped if your fitting a decat downpipe only but it worthwhile doing so imho so you can be sure the car is running as it should be,and that there are no other underlying issues.

Goodluck & enjoy your new ride