difference between cadillac cts sidi and the sfi

DI means Direct Injection of fuel into each cylinder, much more efficient and powerful use of fuel. SFI means Sequential Fuel Injection which means that while each cylinder has a fuel injector they fire into a intake plenum (manafold) sequentially much like Multi point Fuel Injection (MPFI) but which only fires in banks. DI is the only way to go.

Does a 2008 Cadillac CTS SFI make 300 hp?

Now we know that DI cars develop carbon buildup on the intake valves, which port fuel injection can help clean, so manufacturers are increasingly moving towards a combination of direct and port fuekl injection!