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GrimmSpeed Unequal Length Header | 2004-2021 Subaru WRX STI and 2008-2014 Subaru WRX (113026)

GrimmSpeed Unequal Length Header | 2004-2021 Subaru WRX STI and 2008-2014 Subaru WRX (113026)

Regular price $999.00
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2004-2021 Subaru WRX STI and 2008-2014 Subaru WRX Unequal Length Header by GrimmSpeed

Over the years, GrimmSpeed Engineers have proven that we are capable of manufacturing the highest quality, best performing exhaust components for the Subaru aftermarket. While we might not always be the first to release a certain product, our major advantage is that we can take our time in testing and development, putting the product through countless hours and thousands of miles of testing. This ultimately ensures that once a component is in your hands, it will be the most refined version of that product available. The all-new GrimmSpeed Unequal Length EJ Header is a perfect example of this.

The OEM unequal EJ exhaust manifold really hasn’t changed much in the past 20+ years and it shows. The tight geometry and long cross-pipe between the two collectors are not optimized for flow or power, although it does give Subarus their signature sound. While the smaller diameter and volume may be good for low-end spool, the factory manifold gets choked out higher in the rev range. Simultaneously, it's known that swapping to a more-equal length header with larger diameter runners offers additional performance potential. We set out to create a header that would be the best of both worlds, offering great performance and the unmistakable rumble that Subarus are known for!

While other aftermarket unequal length headers use different runner lengths for each cylinder, our proprietary design utilizes an innovative setup where each bank of runners is equal length. One set is 1.5 times the length of the other, providing the rumbling sound that we all love while maintaining the performance of an equal length setup. We utilize single-piece, mandrel bent runners to minimize disturbances to the exhaust gas along with an extremely durable cast 304 stainless steel collector to keep each bank of runners truly equal length, something very difficult to accomplish with a 4-into-1 welded collector. The low-angle merge of this collector makes for a faster spool and unbeatable off-boost throttle response. To match this flow, the collector features machined internal diameters to perfectly match the 1 ¾” primary runners and 2” secondary pipe, eliminating unwanted “steps” in the exhaust flow.

We started the R&D process by scanning the underside of several EJ engine setups using a FARO arm. This allowed us to design and simulate our header in a digital 3D space to find the optimal balance of runner lengths and angles for the best performance possible on an unequal length setup. Next, we were able to 3D-print a number of different configurations to narrow in on the most optimal final design. During this process, we were able to form the header around a variety of different STI oil pan setups, from the factory pan to aftermarket options like those offered by IAG and Killer B Motorsports. After we were satisfied, we made pre-production prototype units that were put through months of punishing performance and longevity testing head-to-head with competitor offerings. During testing, we found substantial power/torque gains over the stock exhaust manifold (+25hp, 25ft/lbs of torque) as well as a quicker spool when compared to the best unequal AND equal competitive offerings on the market. The final result of all this hard work is the magnificent Header you see in front of you.

This Header is the culmination of the Engineering abilities GrimmSpeed has developed over the past 15 years and is as visually stunning as it is efficient in helping your EJ engine deliver its maximum power potential. The aftermarket has a number of other options, but nothing quite as refined as this all-new GrimmSpeed EJ Unequal Length Header.


  • 4-into-1 Low-Angle Merge Cast Collector - Ensures minimal restriction and maximum performance
  • Smooth, Restriction-Free Flow Throughout – Single piece mandrel bent tubing welded to a single piece merge collector removes unwanted “steps”
  • Quickest Spooling Aftermarket Header - Faster spool and more power compared to the competition
  • No Tune Required – Safe to run, just bolt on
  • Gaskets and Hardware Included – Everything you need for installation to get on the road
  • Designed To Fit With Aftermarket Oil Pans - Fits with the STI oil pan or popular aftermarket options
  • Full 304 Stainless Steel Construction - 1/2" flanges and 14 gauge runners for extreme durability
  • Manufactured and Welded In The USA – For consistency and top quality control


  • Substantial Power/Torque Gains - +25hp and +25ft/lbs of torque over stock
  • Innovative 1.5 to 1 Unequal Length Runners - Each bank of runners is equal length, allowing for equal length performance with an unequal length sound

Applications: *Unconfirmed, may require more modiciation

  • 2004-2021 Subaru WRX STI
  • 2008-2014 Subaru WRX
  • 2009-2013 Subaru Forester XT*
  • 2005-2009 Subaru Legacy GT*
  • 2005-2009 Subaru Outback XT*
  • 2002-2005 Subaru WRX (Requires STI oil pan and pickup)
  • 2006-2007 Subaru WRX (Requires STI oil cooler and feed pipe)
  • 2004-2008 Subaru Forester XT (Requires STI oil pan, pickup, and oil cooler)

What's In The Box?

  • 1 - Header


  • GrimmSpeed's Limited Manufacturer's Warranty
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