HuYnHness: you are correct. Horsepower is made on NA vehicles within a certain range ofbackpressure. But if you flow more air in, it needs aless restrictiveway out...

 

yes, it is not right to have too big of exhaust. Mostly for noise. a full 3 inch exhaust would be crazy loud. and yes you will lose backpressure, but anyone willing to put a 2.5+ size exhaust on their car should have an intake at least. this will compensate. more air in plus better flow out equals more power.