1970 318 duster exhaust question???

I put dual 3 inchers on my totally stock long block,73 318. Far as my a$$-dyno can tell,I didnt lose nuttin. And that LC 318 sounds so mellow at full song,pulling through my favorite carb, the mighty TQuad.
EDIT
-I keep hearing this over and over; about your teener with headers,making more torque with smaller exhaust than big. Can somebody point me to the science behind that? Id like to know if my S would go faster and quicker with smaller exhaust than with open headers.And just how far up the cid scale would that apply. For example, If I put a 418 ci or a 518 cid.Would they also go faster/quicker with a smaller exhaust than big?
-And taking that to the extreme,just what size exhaust should the super-stockers of yesteryear have installed to go even faster/quicker than they did?
-Heres my science; go find 2 straws, a regular one, and a supersized one. Blow through them, one at a time. Through which one can you blow more air through, per unit of time? Explain to me how this does not apply to my teener.