Mazdaspeed 3 Exhaust Manifold Break Down

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 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

Mazdaspeed Exhaust Manifold Flange
OEM Exhaust Manifold Flange

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… 

Mazdaspeed Exhaust Manifold Gasket
OEM Exhaust Manifold Gasket

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.  

OEM  Exhaust Manifold
OEM Exhaust Manifold

Designing For Efficiency

In this image, we want to direct your attention to a very unique and troubling design feature of the OEM exhaust manifold.  There is a right way and 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!

Exhaust Gas Scavenging. See the difference between the CS and OEM Manifolds.

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

CST6 | Behind The CorkSport Turbo Design

A few weeks ago we discussed some of the design intent behind the CST5 turbocharger for the Mazdaspeed platform.  Today, we want to follow up with the CST6. The CST5 and the CST6 both were a result of CorkSport’s desire to develop a new stock flange turbocharger that goes beyond the power limits of our FANTASTIC  CST4 Turbo.  

During the development of a higher power stock flange performance turbo, we found that we were asking too much of the CST4 Design.  The result of our efforts is the CST5 Turbo which you can see here and the CST6 Turbo which we are about to dig into.  

In this blog, we’ll dig into the wheel sizing, the CHRA, and some of the challenges we faced in the development and testing stages for the CST6.  

Compressor Wheel

CST6 Mazdaspeed Turbo

The compressor wheel utilized on the CST6 is well-known and trusted, GEN1 GTX76.  The GTX76 compressor is rated for 64 lb/min and is capable of boost pressures that will require a 4 bar MAP sensor upgrade.  Like the CST5, the compressor housing is a 4-inch inlet with anti-surge porting.

Ball Bearing Design

CST6 Turbo Backside

Unlike the CST4 and CST5, the CST6 uses a completely different CHRA and bearing system, and for good reason.  As the turbocharger wheel sizes increase so do the weight and potential boost pressure. This results in higher loads on the wheels, turbine shaft, and bearing system. To increase the durability and performance of the CST6, we opted to move from a conventional journal bearing design for a more modern and robust ball bearing design.  

The ball bearing system improves durability and stability for high horsepower/high boost operation along with improved spool and transient response.  Changing the CHRA did pose some new challenges, however. Ease of installation has always been a key feature with CorkSport products and that’s not lost with the CST6.  The CHRA has been modified to support the use of the OE oil drain line and all necessary oil feed components and coolant components are included for seamless installation.

Compressor Wheel

CST6 Compressor Wheel

Like the CST5 Turbo, we’ve put a focus on the wheel size ratio and have validated its performance. The CST6 Performance Turbo uses the Gen1 GTX76 compressor wheel paired with the Garrett GT35 turbine wheel…aka GTX3576r.  This wheel combination provides us with a ratio of 1.12 which falls well within the rule of thumb discussed the in the past CST5 blog.

In testing, we found that increasing the size of the turbine wheel from a GT30 to a GT35 with the same GTX76 compressor wheel resulted in more top-end power and no penalty in spool time.  This combo also provided a good power delta from the CST5 to better provide an optimal power option for the community. Since then the CST6 has proven power at 600+whp at ~34-35psi and testing will continue past 40psi.  

External Wastegate

CST6 Turbine Wheel

The initial testing of the CST6 started with an internally wastegated turbine housing as that was the original goal with the CST5 and CST6.  However, it quickly became obvious that a turbocharger of this size and power potential could not be safely controlled with an internal wastegate.  The amount the wastegate port and “exhaust” or flow was not nearly adequate for proper boost control.

The boost would creep to nearly 26psi with no signs of tapering off.  Nevertheless, we continue testing knowing that auxiliary fueling was necessary.  Once the CST6 power and durability were validated we moved to design a turbine housing that could provide the necessary boost control and power potential.

Turbo Internal Wastegate Housing

Above is the removed CST6 internally waste-gated housing.  In our testing, we pushed the turbo to nearly 600whp with 40gph of methanol auxiliary fueling.  This amount of heat combined with a turbine housing that was literally being pushed to its limits resulted in a great learning experience.  As you can see, the turbine housing was cracking! The GT35 turbine wheel and power was just too much.

From this discovery and analysis, we developed the EWG turbine housing with the CST6 in mind.  The scroll size was increased, wall thickness increased in critical areas and the 44mm EWG port added.  

CST6 IWG vs EWG

With the use of the EWG turbine housing, boost control is now spot on and can easily control from spring pressure to an excess of 35+psi.  Stick around as we continue to push the limits of the CST6 as we continue testing and validation of the CorkSport V2 Intake Manifold w/Port Injection.  

Thanks for tuning in with CorkSport Mazda Performance.

-Barett @ CS

Inside look: CorkSport Turbo Design

The development and evolution of the CorkSport Performance CST5 and CST6 turbochargers are uniquely intertwined.   We’ll be honest, we started with the goal of a single larger turbo than the CST4 in mind, but as development progressed we were not getting the exact results we wanted. We wanted fast spool & transient response, huge power, and to retain the internally wastegated system.  Something had to give…we realized that we were asking too much from a single turbocharger, thus we redefined what we wanted and realized that two separate and focused turbochargers for the Mazdaspeed platform were the ideal choice.

CST5 Billet Compressor
CST5 Billet Compressor

Today we will focus on the design around the glorious CST5, specifically the theory and design around the wheel selection for the CST5 and why it works.  

CST5 Wheel Design

CST5 Turbine
CST5 Turbine

The compressor wheel utilized on the CST5 is the well-known and trusted GEN1 GTX71.  Compact and efficient, this compressor is rated for 56 lbs/min flow rate with a relatively high-pressure ratio threshold.  Paired with a 4-inch anti-surge compressor housing and we have a very versatile and responsive compressor setup.

Now here is where the design begins to deviate from the standard path.  The turbine wheel is an MHI TF06 design that is designed for high-performance applications.  The TF06 turbine wheel is the key to the performance of the CST5. Let’s see how and why below.

If you are unsure of the turbine wheel size don’t worry, that will get covered shortly.  For comparison, the MHI TF06 is very similar in size to the well-known GT30, but there are a few very specific differences that affect performance.  

Turbine Blades

Turbine Blades
Turbine Blades

The first and most obvious difference is the number of turbine blades; this difference has a couple of benefits. First, less weight; even a small difference in weight can make a significant difference in the spool and transient response characteristics of the turbocharger.  Second, reduce flow restriction; with one less blade, the “open” area through the turbine wheel exducer is increased which increases the peak flow potential for top-end power.

Inducer & Exducer

Inducer & Exducer Comparison
Inducer & Exducer Comparison

Next, are the less obvious differences.  The GT30 has a 60mm inducer and 55mm exducer which equates to an 84trim turbine wheel vs the TF06 with a 61.5mm inducer and 54mm exducer which equates to a 77trim turbine wheel.   

There are two key values to pull from this:  First, the turbine wheel inducer directly relates to the peak flow of the wheel and the overall wheel size balance which we will cover next.  Second, the turbine wheel trim affects the spool and response characteristics of the turbocharger. The smaller the wheels trim the faster the spool and response.  

Sizing

CST5 Sizing
CST5 Sizing

Alright here is the most important and commonly overlooked aspect of a turbocharger.  There is a rule of thumb when sizing the compressor and turbine wheels for a turbocharger.  

If the turbine is too large then the turbocharger will be very “lazy” and have trouble building boost.  

If the turbine is too small then the compressor may be overpowering the turbine wheel causing excessive exhaust gas buildup that can rob power even though you may be running a very high boost pressure.  

So what is the right balance?  From our experience in turbocharger design, development and validation along with industry professionals we have consulted there is a rule of thumb we have found when sizing the compressor and turbine wheels.  The exducer of the compressor wheel should be 10-15% larger than the inducer of the turbine wheel as shown in the image above.

CST5

So why does this work?  Well, let’s look back a bit first.  Many think you can just install a larger and/or higher flowing compressor wheel onto the turbocharger to make more power.  Now that is true to a point, but quickly the approach becomes very inefficient for the engine. Forcing more air into the engine without improving the flow out of the engine can only go so far.  

Everything that goes into the engine must come out, right?  Increased A/R sizing and turbine wheel sizing is the key to exhausting all the gases from the engine efficiently, and efficiency is key to making power.

With both the CST5 and CST6 development we focused on the overall performance of the engine, not just the development of a high-performance turbocharger.  

Thanks for tuning in with CorkSport Mazda Performance, more to come…

-Barett @ CS

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

Mazdaspeed Turbo – Choose Your Boost

May of 2015, CorkSport launched its first high performance drop-in turbocharger for the Mazdaspeed platform.  Fast-forward almost 4 years and CorkSport again is about to redefine what a stock flange turbocharger for the Mazdaspeed platform can truly be.  

The original “CS Turbo” is now the CST4 to follow the turbo line-up that is soon to launch.  The CST4 took a fresh approach to “big turbo” with all the included hardware, gaskets, and of course direct drop-in fitment.  It removed the guess work for a quick and easy installation, but the benefits didn’t stop there. This “little big turbo” packs a punch for its compact TD05H-18G wheels.  

With the CST5 and CST6 just around the horizon it would be easy to forget about the tried and true CST4, but don’t worry this Mazdaspeed Drop-In Turbo got some new love also.  You will now have a EWG housing option for the CST4. You can pick it up in EWG setup from the start or if you already have a CST4 that you love, you can get the EWG housing kit to do the upgrade yourself.

Moving onto the CST5 & CST6 the possibilities for the MZR DISI have moved up significantly.  What started as a single “bigger big turbo” has morphed into two “bigger big turbos” that, we feel, better provide for the various power goals of the community.  

We present to you the CST5

The CST5 bridges the gap between drop-in performance and big turbo power.  The journal bearing CHRA uses a hybrid TF06-GTX71 wheel setup that provides more top-end than the CST4 with minimal spool and response penalty.  Upping the big turbo feel is a 4in anti-surge compressor inlet which will require an up-sized intake system.

Unlike the CST6, the CST5 will be offered in both internally waste-gated and externally waste-gated setups.  This provides you with the flexibility to setup your Mazdaspeed just how you see fit and both have been proven 520+whp on our in-house dyno and tuning courtesy of Will Dawson @ Purple Drank Tuning.

Now… We present to you the Stock Flange Record holder…the CST6

Image: Mazdaspeed-6-big-turbo

The CST6 redefines what the community thought was possible from the stock turbine housing flange, but first some details.  The ceramic ball bearing CHRA uses a GTX3576r wheel setup that clearly out powers the CST4 & CST5, but that’s point remember?  

The CST6 is a legit big turbo, spool will be later, but still sub 3900rpm for full boost, however a turbo setup like the CST6 is not intended for low-end response.  If top-end power is your goal, the CST6 will deliver. In-house testing has pushed the CST6 to 633whp at a fuel limited ~33psi and 7900rpm redline.

Unlike the CST4 & CST5, the CST6 will only be offered in EWG setup.

In the coming months, we will be sharing more information about the CorkSport Turbo Line-Up; the design, the testing, and validation of each.  For more information about the CST5 & CST6 along with the new EWG turbine housing option, check out these sneak peek pages.  

Thanks for tuning in with CorkSport Mazda Performance.

-Barett @ CS