[SabreKhan]

It sounds like he's a drag-racer, though, so he may want to save his pennies and do a full-on turbo upgrade by getting the turbo, the injectors, the fuel pump, the intercooler, the timer, the management system, and the gauges. Doing it all at once will make it a system upgrade rather than just a Ship of Theseus style component upgrade. I don't know what he's got already, though, and I don't know what his uses will be, so I can't make specific recommendations.