Larger injectors are not necessarily needed when upgrading from a carburator to an injection system. The size of the injectors needed depends on the fuel needs of the vehicle. Small sized engines, in the 230 cubic inch range, would need a single, high capacity injector to replace a double barrel carburator. Larger engines would require two injectors. Replacement of a carburator with injectors means that the throttle body would hold the injectors (central or throttle body injection), and the fuel delivery system would need to upgraded because injectors require a high-pressure fuel delivery system.
For more info, see Your Guide to Tuning Carbs