3" exhaust? 2.5" exhaust...??

340doc said
I had 2 1/2 with turbo mufflers on my streeter running 11.70, friend had a 3" system with flowmasters for sale. Spent the money and put it on with no change in ET. Should have saved the money!

So you put 2 totally different systems on a car, didn't change the tuning, and saw no changes. In your mind this results in a theory proved true?