Abstract: An adjustable racing injector injects fuel by carrying out an opening and closing of a fuel orifice in a valve seat. The fuel orifice is controlled by a signal, typically provided by an engine control unit, which energizes a magnetic circuit including coil which in turn will effect movement of a needle. The adjustable racing injector is field reconfigurable and may be provided as discrete components, or may be provided as an assembly together with a collection of replaceable components that are designed to controllably alter the performance of an engine to which the injector is attached. All of the performance components may be readily replaced in the field, while still obtaining repeatable performance across a plurality of injectors.