I think the reason is becouse fluids follow a different set of rules then gasses in terms of flow. By that I mean fluids produce more friction then gasses.

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I think you mean cross sectional area not surface area. Those duals have a ton more surface area in the pipes to create friction witch resists flow. Also because the cross section is so much higher in the duals it loses velocity. If you had two exhaust systems of equal cross section then the single would make more power. The single would also be more balanced and scavenge better, sort of like an X pipe but it don't seperate back appart. A single exhaust with an equal cross section will have more velocity, flow and HP. Your examples are not equal though


This is a very reasonable explanation. I would like to see a dyno test between a dual 2.5" vs a 3" system, but I cant find any examples.

Car in question is a 73 Vega, but I'm sure this theory has universal applications

When it takes more than a sweet mullet to prove you rule at the trailer park..