Let me explain what I think, and you correct me if I'm wrong. Power adders, like blowers and nitrous, actually add horsepower to an engine. In contrast, bolt-on modifications free-up horsepower by using aftermarket parts that are more efficient than the cost-effective factory parts. For the intake, this may include a cotton air filter, true-flow inlet pipe, and larger tb and plenum. By using these aftermarket intake parts, you are not adding horsepower but reducing the amount of horsepower used by the engine to draw air. This horsepower can then be used to move the car forward more quickly. For the exhaust, you can install headers, high-flow mid-pipe, and cat-back exhaust. Again, you are not adding horsepower, but reducing the amount of horsepower that is used to push the exhaust out of the engine. And again this horsepower can be used to move the car forward more quickly. Therefore, aftermarket performance parts are more efficient than stock parts. But, rather than adding horsepower they free-up horsepower that is wasted by inefficient factory parts. If this is true, then the horsepower was already there but wasted on drawing air and pushing exhaust. This also means that bolt-on modifications should not put greater stress on your internal parts than was already there. What do you think of my explanation? What am I missing?