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Part:   21-478WR

AEM 21-478WR Cold Air Intake

AEM Cold Air Intake System
Rating Star 1 Rating Star 2 Rating Star 3 Rating Star 4 Rating Star 5   4.9
  • Increased horsepower
  • Tuned and dyno-tested to improve acceleration and engine sound
  • Low restriction aluminum tubing
  • Easy to install using commonly available tools
  • 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

The AEM 21-478WR fits some Subaru Impreza WRX, Subaru Impreza WRX STi, Subaru WRX, and Subaru WRX STI models. See vehicle applications for details.
The AEM 21-478WR 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 Subaru WRX, WRX STI, Impreza WRX and Impreza WRX STI 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 located in the original air box space and is protected by a heat shield which is designed to reduce intake air temperature and increase horsepower. The intake tubing is constructed from mandrel-bent aluminum featuring a durable textured red powder coated finish. This air intake system was developed to accommodate the engine’s factory emissions control devices including the mass air flow sensor. The 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 easy to install with commonly available tools and it 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 21-478WR vehicle applications to determine the legal status for each vehicle.

[More Information on AEM Cold Air Intake Systems]
Specifications AEM 21-478WR Product Specifications
Estimated Horsepower Gain36 HP @ 5300 RPM
Replacement Filter21-2029DK
Air Filter ColorRed
Air Filter MaterialNon-woven Synthetic
Air Filter Outlet ShapeRound
Clamps Included3
Clamp MaterialSteel
Clamp StyleRegular
Couplers IncludedNone
Product StyleAEM Cold Air Intake System
Air Filter Height9.125 in (232 mm)
Intake Pipe Color / FinishWrinkle Red
Intake Pipe MaterialAluminum
CARB EO NumberD-670-21
Street Legal In All US StatesYes
TUV Approved (Europe)No
Weight7.4 lb (3.3 kg)
Air Filter Large End Diameter6 in (152 mm)
Product Box Height12.25 in (311 mm)
Product Box Length20.25 in (514 mm)
Product Box Width12.25 in (311 mm)
Mounting Hardware IncludedYes

Horsepower gains based on similar vehicle dynamometer test. Results will vary.
WARNING: Cancer and reproductive
Reviews Product Reviews

Sebastian Cianciolo from Ellicott City, Maryland
December 10, 2017 - Part 21-478WR
Easy install. I updated the mapping using COBB input and felt performance gain... not sure how much, but smoother performance and easier and faster spool up. Good price and overal nice gain.
Anthony Ruffini from Moravia, New York
October 2, 2016 - Part 21-478WR
I am very satisfied with this system. There is a noticeable improvement in horsepower and throttle response on my 2009 Subaru WRX. I highly recommend this product.
Kevin Meehan from West Hurley, New York
May 24, 2016 - Part 21-478WR
While not a mechanic, I decided I could install this myself. Let me just say it wasn't quite the piece of cake I was hoping for, due mostly to a very tight fit (both a curse and a blessing). Beyond that, the one thing I can say for sure is that after 3 weeks, there is no question I'm getting better mileage.