New 3" exhaust with 2.5" Tailpipes

A was right out of the headers, B was in front of mufflers, C was out of mufflers, and I think D was at end of tailpipes.

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The data looks cut and paste to me. How can the #'s for 2.5 vs 3 be the same. 3 inch pipe would lose heat faster than 2.5. Disadvantage of 3 vs 2.5... 3 is HEAVY