The stock airbox (drop-in) is much more restrictive than the conical. More air = more power. You can build your own Cold Air Induction for relatively cheap, or you can buy one already made. Thrasher, MSP, SLP, all make CAI's. IMHO its one of the best cheapest mods you can do for your car. And you usually get better gas mileage too, at least I did....
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Chris Jarrett
99 Black GTP
14.35@ 95
Fully Loaded
Reflective Badges Everywhere, S.S. Grilles, Thrasher CAI,
Painted Calipers,
180 T-stat, titanium tint,Blazertech 3200's, ASP 3.4
Chinny's Rims