Well i understand what he means as testcourse gives u the most BHP per race out of all the available tracks, i gained like 7bhp for my evo by doing testcourse(15), i tried a similar thing for midfield(15) and gained 4 with another evo, yes the cars were relatively fresh.
Right. I'm going to theatrically slap my forehead at this point.
Darin - your save game replay/setting file is simply a left-over from the Japanese version. The game converts the power of the car in your garage (which it thinks is in PS - as it is in the Japanese version) into hp (PS to hp = multiply by 0.986). Your Silvia really has gained that power.
Everyone else, go and read BadBatsuMaru's thread called "Everything you always wanted to know about HP, break in, and oil changes", which will tell you, amongst other things, everything you always wanted to know about HP and break in. I've linked it here for you:
Now there really is no excuse for any further speculation in this thread about what may/may not be happening. It's ALL explained in that link. There wasn't much of an excuse in the first place, had but one of you used the