[TurboKraft]

Upgrade the oil pump and piston squirters, and you've got a great foundation for a Turbo engine.

EFI+ITB *and* pistons & cams, and lightweight rods (or at least rod bolts) and that's a fun non-turbo engine capable of 280-300hp on pump gas. Like a 3.0L GT3RS. Won't murder the 915 transmission, either.

But any version of Turbo pistons, with EFI and standard 930 go-fast parts (headers, GT35R, intercooler) and it'll make 500whp without hardly effort. You'd probably have to neuter it with a standard 930 J-pipe turbo-WG pipe and a K27 to keep the 915 in one piece.