A motor is an air pump. The amount of air it can suck in and then pump out is *basically* how much power it can make. Just because you stick a larger diameter pipe on the intake side of an LS motor, doesn't mean it's going to be able to suck more air through that pipe. It'll suck in basically the same amount of air, just at a lowed velocity because there's more volume in the pipe.

Basically, the smaller diameter pipe is already more than enough available airflow for all but the most heavily modified LS motors and the larger pipe just provides more headroom rather than an increase in the amount of air going into the motor.