That's a cheap junk fan. It's too small, and the shroud is there to increase profit margin. Poor shape and the fan opening is too small relative the radiator area.
A dual fan Ford contour setup is 3400-4000+ cfm on full tilt at 12v. That's for an 4 cylinder with AC and is OEM designed with a good bypass ratio. That derale setup is 1800-2400cfm. It would be marginal in almost every case for a hopped up V8. Add the restrictive and poorly shaped shroud and it's about like blanking the radiator with a sheet of plywood.
