Big bore throttle bodies usually don't help much at all unless you have significant improvements to airflow already, i.e, ported/polished head, big turbo, new IC, ported intake, etc... its usually one of the last upgrades considered on something like that.

The reason throttle response is improved is because since the bore is larger, the same input on the accelerator pedal translates to more air entering the engine through the TB...

I'd spend your money somewhere else, on a nice 3" exhaust, or a new IC. You can get a Ford Powerstroke IC for the $250 that the throttle body costs.
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