Will cutting off the muffler cut gas milage?

i have an '83 Ford F150, i want to make it ear shatteringly loud, but not wanna mess with the mileage I have. It didn't come with a catalytic converter, and i was planning on cutting off right before the muffler and leaving it. Where i would cut it is bout halfway down the truck where cab and box meet. Anyone foresee any problems?

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