The Design – 2.5L SkyActiv-G Exhaust Header

CorkSport 2.5L SkyActiv 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

OEM Part Breakdown: 2.5L Skyactiv-G Exhaust Header

Analyzing an OEM part is usually our first step in creating a new performance part. We’ve been looking at the Mazda 2.5l SkyActiv-G Exhaust Header, and I wanted to bring you all along for the ride. It’s surprisingly complex for an OEM manifold/header and some serious engineering went into it.

If you’ve been paying attention to the CorkSport channels, you may have seen rumors here and there of a race header for the GEN3 Mazda 3 and Mazda 6 2.5L. While I can’t say too much on that just yet, but I can give you a breakdown of the OEM exhaust header that’s hiding in the back of your engine bay.

The OEM Exhaust Header

Stock Gen 3 Mazda 3 Exhaust Header
Stock Gen 3 Mazda 3 Exhaust Header

Excuse the dirty part, as this OEM header has had a hard life! I imagine many of you have not seen the stock header as it’s in the back of your engine bay surrounded by heat shields. Taking the heat shields off gives us a glimpse of the craziness that is the stock header. Mazda has gone with a true 4-2-1 design (also known as tri-y) with an integrated catalytic converter and what appears to be equal length runners. Stay with me, I’ll explain what all that means.

SkyActiv-G Exhaust Manifold Flow Path
Exhaust Flow Path

The image above hopefully helps you visualize the 4-2-1 design. Starting at the engine, there are four exhaust ports from the head. Each exhaust port gets its own pipe, known as a “primary”. The primaries then pair together to form two “secondaries”. Finally, the two secondaries combine into one collector pipe, in this case heading directly into the catalytic converter. The three unions or “y’s” are where the tri-y name comes from. The 4-2-1 design was chosen by Mazda for a very specific reason. Check out the image below and Mazda’s explanation HERE.

Mazda SkyActiv-G Exhaust Chart
Residual gas reduction by 4-2-1 exhaust system – From Mazda.com

Essentially, using a very high compression ratio causes very high exhaust gas temperatures. If too much of this exhaust gas is leftover in the cylinders for the next combustion cycle, knocking can occur. In addition, if you have a short 4-1 header or a log-style manifold you can suck exhaust gas into a cylinder before combustion as one cylinder can be on an intake stroke while another is on an exhaust stroke (see the upper image in Mazda’s diagram).

OEM Design Efficiency

The 4-2-1 has two benefits to fight this. First, the long length means the exhaust gas takes longer to traverse the pipes, so one cylinder sucking in another’s exhaust is drastically reduced. Second, the cylinders are paired correctly to one another (1 with 4 and 2 with 3). Since the firing order is 1-3-4-2, each secondary is receiving an exhaust pulse at a regular interval. If you paired 1 with 3 for example, you would receive two pulses quickly, and then a large gap as the other two cylinders fired. This helps with exhaust scavenging as the pulse from one cylinder helps “pull” the leftover exhaust from the cylinder it’s paired with. These benefits can also be present on a long tube 4-1 if designed well but, there is a good reason why Mazda did not choose this option.


2.5L Skyactiv-G
2.5L Skyactiv-G

Typically a well-designed 4-2-1 will make more power and torque in the midrange while a well-designed 4-1 will make more power way up at the top of the RPM range. Since normal driving does not involve being at the top of the RPM range all the time, it makes sense that Mazda went with the 4-2-1. We will likely do the same as we want to retain the low knock characteristics of the 4-2-1, high midrange power & torque, and because the SkyActive 2.5L is a fairly low revving engine.

OEM Exhaust Header 4-2-1 Design
OEM Exhaust Header 4-2-1 Design

It appears that Mazda also went with close to equal length runners. This means that each primary section is the same length and each secondary section is the same length. Having equal length runners ensures the exhaust pulses are arriving at the collector (or Y) at uniform intervals.

The easiest way to explain why this is a good thing is by visualizing the entrance ramp to a highway.  When cars entering the highway follow the “zipper” method for merging, the cars currently on the highway do not need to slow down. The highway and entrance ramp merge and flow in a smooth and consistent rate. However, if a surge of cars come down the entrance ramp to merge onto the highway you will get a back-up of cars on the entrance ramp and will disrupt the flow of cars on the highway.  If the cars are exhaust gases and the highway is the exhaust pipe, you can understand why equal length can help. Again, we will adopt this strategy with the CorkSport Race Header.

So far so good then, as Mazda has put a lot of thought into making a high-quality stock header. However, as usual, there are a few areas we can improve on. That’s coming in a later blog though so you’ll have to stay tuned for more details! Let us know if you have any questions or thoughts down below.

-Daniel @ CorkSport

Corksport Aluminum Crank Pulley for 2.0L & 2.5L SkyActiv Engines

Feeling like your SkyActiv powered Mazda isn’t getting the “shining” attention it deserves? Maybe you’ve already bought every CorkSport item you can, but just want more! I can’t blame you really; it’s a virus that all car fanatics fight.  So here’s fuel for the fire! Introducing the aluminum crank pulley for 2.0L & 2.5L SkyActiv engines!

Screen Shot 2014-12-18 at 1.54.58 PM

Manufactured from high-grade 6061-T6 aluminum, this precision machined crank pulley is sure to give you that extra level of detail you’ve been searching for. Plus it’s 100% designed and manufactured right here in the Pacific NW, USA.

Screen Shot 2014-12-18 at 1.57.41 PM

This crank pulley isn’t just for looks folks, it’s got bite too!  With a 68% weight reduction, compared to the OEM component, your engine is going to rev faster due to the lower moment of inertia of the rotating mass.  I can’t guarantee your bum will feel the difference, but your 2.0L will.

You may also be wondering: “The OEM component is steel, will the aluminum be strong enough?” Absolutely! We’ve been testing the component on an employee car for 2 months (roughly 2000 miles) without a single issue. The accessory belts put a very small, almost insignificant, amount of force on the pulley.  The real concern is the bolt that holds the pulley on, but we got that covered also, see below.

corksport-mazda3-crankshaft-pulley-isometric-vonmises-stress-psi-700x586

To be confident in the products we produce, we conduct FEA (Finite Element Analysis) on all applicable components.  In this case it is the bolt clamping force holding the pulley on the crank.  The crank pulley bolt is an M16x1.5 with a torque spec of 67-80 ft-lb.  For this analysis I used 79 ft-lb which creates a clamping force of 7557 lbf.  Looking at the color graph to the above, you can see that the maximum stress is ~12420 psi which is far below the material yield strength of ~40k psi.  So what does this mean to you? You can (but shouldn’t) torque that bolt down to ~250 ft-lb without worrying about your beautiful new pulley being structurally damaged, but you will have to worry about getting that bolt out next time, that’s your own problem.

Crank Pulley

Add some shine to your engine bay and just a little more pep in your step.  Keep an eye out for the product release in the near future! Offered in anodized black.  Zoom – Zoom!

Barett – CS Engineering

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Product Release!! CORKSPORT 2010+ Mazda 3 Skyactiv Air Box for CorkSport SRI

Help limit your CorkSport Short Ram Intake from sucking in hot air with the CorkSport SkyActiv Cold Air Box for the 2010+ Mazda 3 Skyactiv. By coupling your Short Ram Intake with a cold air box, you will see the benefits of the intake system without the pressure drops inherent to longer tube intakes. Using the CorkSport Cold Air Box helps block hot air from the engine, while keeping open the access to cool air from the inner fender.  Our Cold Air Box has undergone extensive testing at various ambient air conditions to verify performance in all conditions.

CorkSport SkyActiv Airbox

Made of durable and lightweight FRP construction the CorkSport Mazda 3 SkyActiv Air box is strong and lightweight, but looks great under your hood. Simple instructions make the CorkSport SkyActiv Air box easy to be installed by anyone with a CorkSport Short Ram Intake. With the SkyActiv Airbox your intake will stay cooler, which means your engine will run better. Whether you sit in a lot of traffic, live in a hot climate, or simply have noticed too much heat-soak, the SkyActiv Air box is the solution to loss of power due to high under hood temperatures.

SkyActiv-Airbox-Installed

 

The CorkSport 2010+ Mazda 3 Skyactiv Air Box for CorkSport SRI is available at our online catalog for only $99.99 and is ready to ship now. For more information please visit our product listing at:https://www.corksport.com/corksport-2010-mazda-3-skyactiv-air-box-for-corksport-sri.html