The CST6 has Arrived!


The long wait is finally over and you can now get your hands on the CorkSport CST6, which holds the record for the highest horsepower on the OEM turbine flange at 684WHP! In case this is the first time you’ve heard “CST6”, be sure to check out our blogs on the CS Turbo catalog, CST6 Design, and CST6 Testing. The CST6 is truly a big turbo, so if you’re ready for some serious power on your Mazdaspeed 3 or 6, read on!

CST6 with External Wastegate for Mazdaspeed

Let’s start by looking at the anatomy of the CST6. The backbone is a tried and true dual ceramic ball bearing Garrett CHRA. We opted for ball bearings to improve response and durability, especially when running at high boost levels the CST6 is capable of. As for wheels, the turbine is a 10blade GT35 while the compressor is an 11blade GTX76 that is rated for 64 lb/min. This combo provides fantastic spool characteristics for its large size, achieving 20psi by 3800-3900 with the appropriate supporting mods and headwork like on Barett’s GEN1.

Mazdaspeed Turbo

The quick spool is not due to the wheels and ball bearings alone though. A lot of research and development went into making the turbine and compressor housings the right fit for the CST6, and balance fast spool with top-end power. A 4” inlet with anti-surge ports provides plenty of air into that compressor wheel while a high swallowing capacity 0.82 A/R external wastegate turbine housing offers superior top-end power capabilities and optimum boost control. Even with all these changes, the CST6 fits in the OEM location; all you need is the external wastegate actuator and an intake that fits the 4” compressor cover.

CorkSport CST6

The CST6 is definitely not all bark and no bite though. We have thoroughly tested the CST6 up to its limits and beyond and have had nothing but success. Check out the graph below, that is the CorkSport CST6 in “calm” trim making mid-500s at 28psi. The difference in power on the graph was a back to back exhaust manifold change but more on that when we reveal more of the CorkSport Exhaust Manifold….

CST6 Dynograph

At the limit of the CST6 is a full bore 38psi, port-injected E85, and revving out to 8000RPM, resulting in 684.7WHP and 552WTQ. Check out the graph below. There may even be a little more to be had, with a larger 4” intake and 3.5” downpipe and exhaust.

CST6 Dynograph

Like every other CorkSport turbo, the CST6 comes with all new hardware, gaskets, and the needed oil and coolant lines to make your install as painless as possible. The CST6 is a little special though as it also comes with a v-band clamp and EWG elbow to help with the installation of your EWG actuator. While you will have to supply the EWG actuator itself, the elbow helps locate the Tial 44mm (or equivalent) wastegate in a usable location, whether you have an MS3 or MS6. In addition, we have a dump tube available for purchase to prevent any fabrication on your CST6 install.

So if you’re in the market for some serious horsepower on your speed, be sure to check out the CorkSport CST6. Let us know if you have any questions on the CST6, installation, or supporting mods, we’re happy to help!

P.S. If you buy a CST6 share your power graph with #CorkSport

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

CorkSport CST4 vs. OEM K04

For the last four years, we’ve been asked countless times if the CST4 is a direct replacement for the OEM K04. With the number of cars experiencing their 2nd, 3rd or even 4th owner, this question is being asked more frequently.  While CorkSport’s intent is to freely share information across the Mazda community, we cannot be everywhere all at once, and we will most likely miss the exact moment the debate explodes on your favorite Facebook page. For that reason…

Today, we’re setting the record straight: The CST4 is a drop-in UPGRADE from the ground up, and by no means is it an apples to apples comparison with the asthmatic K04.

How Does It Work?

Before we dive into the dirty details, you might be craving more details on how a turbo works? You are in luck! Check out our white paper on the CST4 and what makes up the anatomy of a turbocharger, bone up on the importance of a “bolt-on” vs a “drop-in” turbocharger, learn the difference between an internal vs external wastegate and finally why the turbine wheel design/materials make a difference. Now let’s get back to what this means for the CST4 and K04.

CST4

Is The CST4 Reliable?

The CST4 continues to prove itself as one of the best bolt-on options coupled with the needed reliability to withstand the additional demands of chasing 400 WHP  – something the KO4 cannot accomplish. This is due to an upgraded center housing rotating assembly (CHRA) which has a larger center shaft and larger bearings than the OEM turbo. The CorkSport turbo also sports a performance journal bearing with a full 360° thrust collar, which is what allows the turbine shaft and compressor to spin freely. The OEM K04 turbo comes standard with a limited 270° thrust collar.

Does The CST4 Have Increased Airflow Over The K04?

CST4 specs vs. k04 specs

Next comes wheels, which is where the CST4 really shines. Shown in the image above, we have the CST4 on the left and the OEM K04 on the right. The CST4 is 12% larger on the compressor inducer, and 21% larger on the exducer than the OEM K04. Combined with the use of a taller wheel (green line), every revolution of the CST4 not only brings in a greater quantity of air into the compressor, but has a higher airflow capacity, thus moving a greater volume of air. For those of you that need a few more key specific numbers; The OEM K04 uses a 45mm inducer; 56.25mm exducer cast compressor wheel, while the CST4 uses a 50.5mm inducer and 68.1mm exducer forged billet compressor wheel.

On the turbine side, the OEM K04 uses a 50.1mm inducer and a 44.5mm exducer 12-blade cast wheel. The CST4 uses a 56.2mm inducer and 49mm exducer high-flow 9-blade design. Again, the CST4 outshines the K04 with the turbine inducer being 12% larger and the exducer 10% larger. The 9-blade design has two key benefits: more peak exhaust flow as there is less material in the way of flow, and 21% lighter for a faster spool time.

CST4 Side View

The final component is the compressor and turbine housings. The K04 uses restrictive housings that cannot keep up at higher RPMs, and especially at higher boost levels. You can feel this as your stock turbo “runs out of steam” up above ~5200RPM. The CST4 housings may fit exactly in the OEM locations and use the OEM hook up points but that is where the similarities end.

Both the compressor and turbine housings were increased in size, increased in A/R, and optimized for the stock inlet and outlet sizes to provide better top end capabilities. The compressor ended up at a 0.53 A/R while the turbine ended up at a 0.66 A/R. This combo of housing and wheels keeps power all the way to redline, and in initial testing showed a 50WHP gain at the same boost pressure.

How Much Power Does The CST4 Make?

So what does all of this mean in terms of power? We’ve seen the OEM K04 pushed way out of its comfort zone and make in the 350-360WHP range with the right supporting mods. This is far out of the efficiency range of the little K04, and it’s a ticking time bomb when running at this power level. The CST4, on the other hand, is perfectly happy running in the 400WHP range all day, again, with the right supporting mods. We’ve even seen it pushed to its limit in the 450-460 range.

For those of you more interested in boost pressures, the K04 can hit a max of ~24-25psi in the midrange before it’s out of its efficiency range and starts producing just heat.  At redline, the K04 is typically at a max of about 17-18psi. What you feel as your car seems to stop accelerating after ~5200RPM on the stock turbo. The CST4 does a lot better, hitting a max of ~29-30psi in the midrange but carries the high pressure into higher RPMs, with peak boost pressure at redline of ~26-27psi. This keeps you pushed into your seat with a smile on your face!

CST4 Mounting Point

How Quickly Does The CST4 Spool?

We get a lot of questions on how fast this turbo spools, so let’s take a moment to discuss both. The OEM K04 spools very quickly since its housings and wheels are so small. If tuned incorrectly it can spool almost instantly and kill blocks with an extremely low-RPM torque spike. The CST4 also spools quick, making full boost by approximately 3300RPM on most cars. The big difference is that the CST4 carries power out to redline instead of falling off as the K04 does. To be clear, you still have to be careful with the CST4 as it too can kill a stock block with too aggressive of a tune.

Is The CST4 A Drop-In?

So bringing things full circle, the “drop-in” aspect of the CST4 means you can run it with almost no other supporting parts, only a HPFP upgrade, access port, and a tune are required. It also means that it hooks up directly to the OEM inlet and outlet flanges so that there is no excessive modification required to make the turbo fit. We even include new studs, lock nuts, gaskets, a custom upper coolant line, new coolant and oil crush washers, and the correct oil feed banjo bolt so there is no hassle of finding replacement hardware, gaskets, or lines to make your turbo function. We do strongly recommend picking up a CorkSport EBCS to best control boost on your CST4. We have also found that the stock intake size will be maxed out at around 18-19psi on the CST4. To get more power from there, a 3 inch or 3.5-inch intake will be needed.

By no means is the CST4 a K04 though as it’s larger and has much higher horsepower capabilities. For those of you more familiar with Garett turbos, the CST4 is just a smidge bigger than a GTX2867.

If you want even more info on what makes the CST4 tick be sure to check out the white paper on the subject HERE. As a final afterthought, remember that the CST4 is getting an EWG housing option in the coming months, for added features (and noise!) that just don’t come with the K04. Stay tuned for that, and be sure to ask any questions you may have.

Testing – CorkSport External Wastegate Housing for Mazdaspeed

Turbo EWG

Why EWG?  (it’s just about awesome turbo noises)

We hear this alot as the Mazdaspeed platform continues to grow and the 450-500whp build becomes the status quo. Following up the EWG Housing Design & Details Blog about the new CorkSport EWG Housing, we want to share some testing data and differences we saw between an IWG (internal wastegate) and EWG (external wastegate) setups.  

Details about design, flow, placement, data, and feedback from our CST4 EWG Beta Tester.  

IWG vs EWG comparison on the CST4
IWG vs. EWG on the CST4

Let’s jump right in!  First up is a spring pressure comparison between the IWG and EWG housing on a CST4 turbocharger.  Let’s first define what “spring” pressure is: this is the resulting boost pressure with 0 added wastegate duty cycle.  AKA we are not trying to add boost pressure.

Immediately you can see some very obvious differences.   The IWG setup has a taper up boost curve that could be considered boost creep.  Some boost creep is ok, but an excessive amount may reach the capacity of the fuel system or other systems in the vehicle.  In this setup that is not the case, but it does show that the IWG is at its limits for boost control.

With the EWG setup you see a much different curve.  The boost builds a few hundred RPM later (due to the larger 0.82 A/R) then climbs right to the spring pressure and then settles to a consistent plateau; very predictable and controllable.  

CAD EWG and IWG Designs
CorkSport EWG and IWG Designs

Now let’s look at the design to better understand why.  On the left is the EWG turbine housing with a 0.82 A/R and on the right is the IWG turbine housing also with a 0.82 A/R (we don’t want the A/R to be a factor in this review).   

The EWG housing has a very efficient flow path for the exhaust gas to reach the EWG control valve along with a much larger path to flow.  Both of these features provide excellent flow and thus control of boost pressure.

The IWG housing uses a side port in the turbine scroll to exhaust gas.  In this setup, the exhaust gas must make an abrupt turn and pass through a much smaller port.  Both of these issues reduce boost control.

EWG and IWG Explained

Here is a diagram showing placement of an EWG in the exhaust pre-turbine.  Granted we are comparing a EWG and IWG, but the concept of flow is the same.  

Exhaust gases will always take the path of least resistance and if the turbine wheel is the easier path than the wastegate then boost control will be more difficult.  

Internal and External Wastegate performance chart
(Left) Internal Wastegate Setup | Common Issues
(Right) External Wastegate Setup | Optimized Setup
Click to Expand

This graph was shown in the last blog, but we want to show it again so you can directly compare it to the data graph below.  

Below is the boost curves for the CST5 in both IWG and EWG setup.  Alone each graph actually looks really good, but when overlaid you can see some interesting differences.  

CST5 Dyno testing with IWG and EQG setup

IWG vs. EWG on the CST5

The purple IWG graph has a crisp spool and then flat-lines at approximately 30psi with a slight fall off at 6500rpm.  The CST5 IWG setup does control boost really well, but holding the turbo back at spool up and not over-boosting or spiking was a small challenge.  An abrupt boost curve like this can make the car somewhat difficult to drive because the torque “hits” very hard and you lose traction.

The EWG setup was a bit more controllable.  Not only did the CST5 turbo spool a bit sooner, but we were able to better control the spool up boost curve so we could create a torque curve that was more friendly to the FWD traction.  This makes the car more fun to drive. Looking at the higher RPM range we were also able to hold boost more consistently to 7500rpm.

CorkSport External Wastegate

We hope you guys and gals are as excited for the EWG options for the CST4, CST5 and CST6.  They really are an awesome setup for any driving style and power goal.  

Thanks for tuning in with CorkSport Performance.

-Barett @ CorkSport

The CorkSport CST5 is HERE!

We are happy to release the new “medium big” brother to the tried and true CST4, the new CorkSport CST5 Turbocharger for the DISI MZR engine found in the Mazdaspeed 3, Mazdaspeed 6, and Mazda CX-7 Turbo. Finding a middle ground between response and top end power is always difficult when selecting a turbo, yet we believe we have nailed it with the CST5. You get the response of a smaller turbocharger yet retain high horsepower capabilities of a big turbo.

CorkSport CST5 Turbo Front
CST5

Before we get into power, let’s first discuss what makes the CST5 tick. It’s all started with a proven MHI journal bearing center section. These offer great cooling capabilities and fantastic reliability, especially when combined with our high performance journal bearings and 360° high performance thrust bearing. The CST5 can seriously take a beating, and does it in a package that fits perfect in the OEM location.

CST5 Billet Compressor
CST5 Billet Compressor

Attached to this center section is a compressor and turbine wheel combo that is a little unconventional. Creating boost is a tried and true GTX71 billet compressor wheel that is rated at 56lb/min. The turbine that drives the CST5 is where things get a little interesting. Instead of a standard GT30 10 blade wheel, we chose a MHI TF06 9 blade design. This offers a number of benefits that make the CST5 outshine a comparable 3071 setup. One less blade means lighter weight for faster spool times and higher maximum flow capacity. The TF06 design is also slightly larger than a GT30, yielding a better wheel size ratio for more efficient turbocharger and engine function. For full info on the wheels and what they mean for your Mazdaspeed, check out our design blog HERE.

CST5 Turbine
CST5 Turbine

The new wheels are wrapped in new housings. On the compressor side, there is a 4” inlet that includes anti-surge ports for optimum compressor operation and longevity. This large size also maximizes efficiency for 3.5” and 4” intakes. The turbine side is where there are the most differences from the CST4. The A/R has been increased from 0.66 to 0.82 which provides more top end power to match the rest of its big turbo characteristics.

CST5 Internal Wastgate
CST5 Internal Wastegate

Now, what does all of this tech mean for you and your car? If you have a stock block you can easily max out power (~400WHP) and stay safe on your rods. Due to the bigger size, the CST5 peak torque is slightly later than the CST4, keeping you safer even before tuning is considered. Having a built block is where things really get interesting. The CST5 will make~450WHP all day on a “calm” boost level of 25-26psi. If you really want to push it though, the CST5 has made ~520WHP on ~30-31psi. This versatility allows the turbo to grow with your build. So even if you are stock block now, the CST5 can carry you even after you build your block.

The wheel and housing options delivers great response as well as great power. When pushed to its limits on a built block, 20psi was hit at 3400-3500RPM with 30psi hitting by a surprising 3700-3800RPM. Obviously this isn’t stable for a stock block but is possible on fully built cars with full bolt-ons and a high flowing head.

CST5 Dynograph Comparison
CST5 Internal Wastegate vs. External Wastegate

The versatility continues as the CST5 is offered with internal wastegate or external wastegate turbine housing options. The internal wastegate setup is the best if you want an easy drop-in fitment with great boost control. The external wastegate setup if you’re willing to take a little bit more time for fitment and spend a little bit more money on the external wastegate itself for the best in boost control. The EWG setup offers some great new sounds from a screamer pipe as well. As for power, they are very comparable, as shown in the graph above. The EWG setup makes just a tiny bit more up at the peak, but that is likely due to small variances in tuning. While only the IWG setup is offered at the time of writing, the EWG is coming very soon! Lastly, if you must have a CST5 now, don’t worry, the EWG housing will be sold separately if you want to upgrade down the road.

Both the IWG and EWG options come with a full hardware kit that includes everything you need for install. This means all coolant/oil lines, new gaskets, new crush washers, and even new studs and crimp nuts for both the turbine and downpipe flanges. The EWG setup includes a custom designed elbow for great EWG actuator fitment on MS3 and MS6, and the correct clamp to attach it to the housing. More info to come later on an add-on screamer pipe option.

CST5 Included Hardware Kit

CST5 Hardware Kit – Included!

Each CST5 also comes with full CorkSport support, including full-color install instructions, a 1-year warranty, and assistance with any questions you may have. We are extremely excited for you all to get your hands on the CST5 and start making even more power so please check out the product listing for full details and to place to order.

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