Not sure if this has been done, apologies if it has.

Say you have 3 WRX as follows (all classic say)....
UK - 220bhp at flywheel before mods
Jap - 240bhp at flywheel before mods
Type R - 280bhp at flywheel before mods.

If you did the same basic mods ie 3inch exhaust with no cats, and cold air flow air intake (to keep it simple), would each WRX get the same %age increase in power, or would the higher powered cars get an increasingly smaller % power gain.

Not sure how this works, any comments ??