They pull hot air in from the engine compartment. They're worse than stock. On a dyno you're ok, because the hood's open and the fan is blowing on it. It'll show some gains. In the real world with the hood down, it's a hot air intake. The stock intake is less likely to heat soak since it's not metal, and the airboxes pull cooler air from in front of the radiator support instead of hot underhood air. That's why drop in filters and MAF tubes work so well. You're still getting cool air.
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2011 MB Touring-Sport-6sp-Nav/GTM TT/FI TT TDX/JTran/Kosmic/Eibach/Hotchkis/SPC/CSF/RPS/SoThatsWhereAllMyMoneyWent
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