Today we want to break down the OEM exhaust manifold for the Mazdaspeed platform so that you can better understand how and why the CorkSport Exhaust Manifold makes power.
If you haven’t heard, CorkSport has been developing a performance cast exhaust manifold for the Mazdaspeed platform. We’ve tested and validated samples on Mazdaspeeds ranging from 350whp to 684whp. We’ve done dyno testing on the OEM exhaust manifold vs the CS manifold, as well as on the XS Power V3 manifold vs the CS manifold with the man, Will Dawson of Purple Drank Tuning, setting the calibrations. Both tests showed good gains from just the CorkSport Exhaust Manifold alone. However, we can get into those details later.
Mazda Exhaust Manifold Design
This is the OEM (original equipment manufacturer) exhaust manifold found on the 2007-2013 Mazdaspeed 3 and 2006-2007 Mazdaspeed 6. Manufactured from cast iron and very compact in design, the OEM design leaves A LOT on the table in the performance department.
In the image, we’ve labeled each cylinder since that will be important for later discussion.
OEM Manifold Exhaust Flow
So now let’s talk flow. Fluids (or exhaust gases in this situation), will always take the path of least resistance. When the flow path is not clearly defined for the exhaust gas, such as a merge between different cylinders, turbulence is created which reduces the efficiency of the exhaust manifold.
A prime example of turbulence is shown in the image above with the orange arrows at the merge for cylinder 1 and cylinder 2. Cylinder 2 comes to a “T” and therefore could flow left or right. This creates turbulence which causes a loss in potential power.
Next is the yellow arrow. This is identifying the inner diameter of the runners in the OEM exhaust manifold. To our surprise, the inner diameter of the OEM exhaust manifold is actually pretty decent at ~1.48 inches. This diameter partially defines the power a manifold can support efficiently. Bigger is better in this situation, but small changes here will make big differences in the final performance.
Surprisingly, there are “performance” exhaust manifolds on the market for the Mazdaspeed platform that have smaller inner diameter runners…
We also wanted to point out an unusual but important aspect of the Mazdaspeed exhaust manifold and gasket. Have you ever noticed the seemingly useless extend flange off of cylinder 4? This extended flange acts as part of the passage for the exhaust gas recirculation port.
You can more clearly see this port path in the gasket.
Designing For Efficiency
In this image, we want to direct your attention to a unique and troubling design feature of the OEM exhaust manifold. There is a right way and a wrong way to pair cylinders on an exhaust manifold for a 4-cylinder engine, and this is the wrong way.
Referencing our cylinder callouts in the first image above; you can see that the OEM design pair cylinder 1 & 2 together and cylinder 3 & 4 together. This design physically works, but it is not ideal from a performance standpoint. In a divided manifold, you should pair cylinders 1 & 4 together and cylinders 2 & 3 together for optimal cylinder exhaust gas scavenging. To learn more about exhaust scavenging you can check out a blog on that here, or watch the video below!
Before we wrap here we do have one good thing to say about the OEM exhaust manifold. It does sound really good and gives the Mazdaspeed platform a unique exhaust note, but don’t worry you don’t lose your unique rumble with the CorkSport design.
Thanks for checking in with CorkSport Mazda Performance. Stay tuned for more info about the CorkSport Performance Exhaust Manifold.
-Barett @ CS
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