[GretchenGotGrowl]

Some mods do add power others simply reduce the losses. An internal combustion engine is a pump. The more air you can get to flow through the more fuel you can add and the bigger the "explosions" you will get. Bigger explosions mean more power. Changing the exhaust manifolds allows more air to flow through and you make more power. Add an underdrive pulley and the accessories run at slower speed and take less power. No power was added to the engine, but less was robbed. In the first case you crank and wheel power went up, in the second only the wheel power went up.

Hope that helps.