AEM COLD AIR INTAKE SYSTEM For 06-11 Honda Civic Si 2.0L - 21-685C

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The AEM 21-685C Performance Cold Air Intake System produces horsepower and torque gains by replacing your vehicle's restrictive factory air filter and air intake housing. This air intake system was designed, tuned and dyno-tested to fit specific Honda Civic SI and Acura ILX models. Air enters the system through an oversized AEM Dryflow synthetic washable air filter for outstanding air flow, filtration and performance. The air filter is relocated to the driver-side wheel well which is designed to reduce intake air temperature and increase horsepower. The intake tubing is constructed from mandrel-bent aluminum featuring a durable gunmetal gray powder coated finish. This air intake system was developed to accommodate the engine's factory emissions control devices including the mass air flow sensor, a couple replacement silicone breather hoses as well as a replacement radiator hose. The tapered cylinder shaped AEM Dryflow air filter is made from an oil-free, synthetic filter media that can be used for up to 100,000 miles before cleaning is needed (depending on driving conditions). The air intake system is backed by AEM's Lifetime Limited Warranty. Some AEM air intakes are not legal for sale or use in California and other states adopting California emission standards, while others are 50 state legal. View the 21-685C vehicle applications to determine the legal status for each vehicle.

  • Increased horsepower
  • Tuned and dyno-tested to improve acceleration and engine sound
  • Low restriction aluminum tubing
  • Air filter lasts up to 100,000 miles before cleaning is required (depending on driving conditions)
  • Washable and reusable oil-free filter media
  • AEM Lifetime Limited Warranty

Installation PDF

Installation Instruction Sheet

Dyno Chart - 2007 HONDA Civic Si 2.0L - 6.27HP Increase


Estimated Horsepower Gain 6.27 HP @ 5100 RPM
Replacement Filter 21-203DK
Air Filter Color Red
Air Filter Material Non-woven Synthetic
Air Filter Outlet Shape Round
Clamps Included 11
Clamp Material Stainless Steel
Clamp Style Mini
Couplers Included None
Product Style AEM Cold Air Intake System
Intake Pipe Color / Finish Gunmetal Gray
Intake Pipe Material Aluminum
CARB EO Number D-670-21
Street Legal In All US States Yes
TUV Approved (Europe) No
Weight 8.2 lb (3.7 kg)
Product Box Height 12.25 in (311 mm)
Product Box Length 20.25 in (514 mm)
Product Box Width 12.25 in (311 mm)
Mounting Hardware Included Yes
Warranty Limited Lifetime


Supported Vehicles

2011 Honda Civic Si 2.0L L4 Gas

All Models

Street Legal in All US States: Yes

CARB EO Number:

D-670-21

2010 Honda Civic Si 2.0L L4 Gas

All Models

Street Legal in All US States: Yes

CARB EO Number:

D-670-21

2009 Honda Civic Si 2.0L L4 Gas

All Models

Street Legal in All US States: Yes

CARB EO Number:

D-670-21

2008 Honda Civic Si 2.0L L4 Gas

All Models

Street Legal in All US States: Yes

CARB EO Number:

D-670-21

2007 Honda Civic Si 2.0L L4 Gas

All Models

Street Legal in All US States: Yes

CARB EO Number:

D-670-21

2006 Honda Civic Si 2.0L L4 Gas

All Models

Street Legal in All US States: Yes

CARB EO Number:

D-670-21

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