I'm not sure but let's try. All added hp's add of cource hp's at the crank and the drivetrain takes ~25% (30 out of 130) of the power. And wheel power will be that 75% of the crank value, no matter how many hp's your engine gives. So drivetrain etc. will take that 25% of every added hp's too. That means if you get 10 hp's with new mods you'll get 7-8 hp's more at wheels.

It's not that you are ADDING hp per say. It's more that your are freeing up power that is restrained due to restrictions in the intake/exhaust system. But you do net more power. Keep in mind that our cars only have the power of 100 weed wackers so don't expect any more than 15-20 hp to the wheels from intake, exhaust, headers.

you DO get more hp on I/H/E mods....the only way that you net more to the wheels without an actual increase is by doing tranny mods,i.e.,lightened flywheel,somehow getting a more efficient tranny,like a manual compared with an automatic will have less whp loss

Even a 2.0 Protege would be lucky to get 15-20 at the CRANK with I/H/E.

Didn't that Traveler dude get about 9hp at the wheels with just a custom header? I forget and he seems to be missing. I read somewhere that the most restrictive part of the exhaust in 3rd gens is the stock exhaust manifold and first catalyst, and a true header that eliminates the first cat could definately give some decent gains, although its illegal. 15bhp doesn't sound unreal, but probably would come in closer to 10bhp.