The Design – 2.5L SkyActiv-G Exhaust Header

A few months ago we broke down the complicated design of the exhaust manifold found on the 2014-2018 Mazda 3 & 6 2.5L SkyActiv.  Mazda put extensive R&D into the design and packaging of the OEM header to optimize the exhaust gas pulses and overlap.  

In this blog we are going to explain some of the design features in the CorkSport 4-2-1 header and why those features are important.  

Below is a diagram showing the primary, secondary and collector routing of the OE header.  

Mazda 2.5L SkyActive Header
The OEM header for the 2.5L SkyActiv engine has a 4-2-1 design.

When designing a performance header we have to ask ourselves, “what is the goal with this performance part?” and then fulfill that goal.  With the performance header for the 2.5L SkyActiv our goal was to increase mid-range torque, retain good fitment and user installation, and improve the sound output of the exhaust system.  

CorkSport Aftermarket Exhaust Header
CorkSport 2.5L SkyActiv header design.

Immediately you’ll notice a significant difference in the design of the OEM header and the CorkSport Header.  There are three major differences:

  1. Primary, secondary, and collector diameters have been increased to promote better exhaust gas flow.
  2. Primary and secondary runner lengths have been increased to optimize power/torque lower in the RPM range.
  3. The design is two-piece to drastically improve the installation process.  

The primary runners (these are the runners that mate directly to the engine) have been increased in diameter from 1.55” to 1.75” and the secondary runners (these are the runners that combine only two cylinders before the collector) have been increased in diameter from 1.87” to 2.00”.  Both of these changes improve peak flow per cylinder throughout the RPM range. Lastly, the collector has been increased from 2.00” to 3.00” to be paired with the CorkSport 60.5mm or 80mm Cat-Back Exhaust Systems.

CorkSport Exhaust Header Installed
CorkSport Header Installed.

Here’s where things got a bit tricky.  Increasing the length of the primary and secondary runners forced us to be a bit creative in routing all the piping.  In order to achieve the primary runner length we wanted, we had to route the piping upward first (as you can see below) then back down between the engine and firewall.  The results were better than we expected with a “Medusa” style header peeking out of the engine bay and the lengths we wanted.

It makes us grin every time we pop the hood open, we hope you love it as much as we do.  

CorkSport 2.5L Exhaust Header broken down for install.
The final design of the CorkSport 2.5L header is installed in two pieces.

However, the complicated CorkSport design did create a new problem.  Installation! We always try to create a performance part that can be installed by the average enthusiast in their garage and this was no exception.  In a one-piece design, the header was nearly impossible to install. We went to the drawing board and realized that separating the upper and lower halves of the header was the best option.

We considered a conventional flange, gasket and hardware setup, but realized it to was far too complex in the close quarters behind the engine.  We then moved to a v-band connection that proved to be the best setup for installation, weight, and sealing ability.

That wraps up the design, next we’ll breakdown the testing and results! Let us know if you have any questions or thoughts down below.

-Barett @ CorkSport

20 Replies to “The Design – 2.5L SkyActiv-G Exhaust Header”

  1. Will this increase under hood temps? Also
    Will this interfere with the strut tower bar?

  2. Love it! Want it! But what about the cat? I put in your guys exhaust and it deleted the 2nd cat. Now if I get the header it will delete the first cat. What will that do for emissions?

  3. Will the header come with hardware and gasket or will we need to provide our own?

    Will it bolt up to the stock and/or 60mm mid pipe/catback.

  4. So what are the before/after lengths of each section of the header? Do you also have any data on if the average engine bay temperature while driving has increased?

    And when does the next blog land?!

  5. Will this be for both ATX and MTX?
    Possibility of CARB legal for California??
    Package deal for the turbo kit as well??
    Ohhh so many questions.
    Like a 6 year old on Christmas waiting to open presents.
    Would love to get one ASAP!!!

  6. MTX is the only option currently. This is a race header so there is no chance of a CARB #.

    The header and the turbo kit go in the same place so you would have to choose one or the other.

  7. I just tried to find this on their website and it wasn’t showing up, where could I buy this header at?

  8. Would this fit in a 2018 CX-5? It looks like the exhaust manifold is the same on there as it is on the 6 2.5

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