do I need the plastic deflectors under my bumper?

The Mach 1 Chin spoiler fits ahead of the air deflector on the SN95 Gen2, but it would seem it would deflect air in through the bumper opening. Without the chin spoiler, as noted above (agreed, great post), low pressure is created to feed the radiator. Remember, these newer cars are 'bottom feeders' without a large grill opening.