Leave it on, unless you plane on replacing it with a different one. The Z (coupe) looks naked without it. Also, if you lower your car, that too has an effect on the aerodynamics. The 'lift' effect at high speeds is very real and most cars are designed with zero lift in mind. Race cars are designed with downforce, trading more 'drag' for more grip. For most street cars, they design them to be neutral or zero lift for better fuel economy.
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[09][MB][6-Spd MT][Touring][Stillen Gen III][K&N][Borla CBE][Evo-R]
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