an engine breaths because in reality it is nothing more than an air pump. an engine moves it's displacement of air in one cycle. that's why we have 2 and 4 cycle (stroke) engines. A small block chevy 350 breaths 350 cubic inches of air in one cycle. changing intakes or cams or exhast allows for superior fuel mixtures to occur.
I would question your mileage increase by just removing a item that is basically a hollow pipe. The mind is a wonderfull thing.
Wish you had posted the actual miles per gallon you're getting on the highway. When you get up to 32 MPG let me know as we have the same motor as you in a 99 Grand Prix with nearly 100,000 miles on the odometer.
If removing the resonator helped that much try a u-bend delete, or better yet a set of headers.
I have a 2004 chevy monte carlo SS with a 3.8L V6 engine. and about a year ago i upgraded the air intake system to a full K&N intake system. got maybe 2 mpg... but last week i was interested in opening up my exhaust and having a more throaty sound to it... so the mechanic suggested taking out the resonator and that will give me the sound i'm looking for. now I read mixed reviews on this and most say that i will lose mpg. But i noticed after taking out my resonator, i am getting quite a boost in mpg... maybe 3.5-4 mpg! and i'm also getting extra horsepower. i noticed that my car takes off a little faster, it seems.
