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, let’s go over how a turbo works. A turbo is comprised of three major sections: the turbine, the center housing rotating assembly (CHRA), and the compressor. The compressor brings in clean air, and as the name implies, compresses the air before sending it through the CHRA and into the cylinder intake. With extra air in the cylinder, the engine is able to burn fuel at a faster rate. This process creates exhaust, which leaves the cylinder and is sent past the turbine, causing the turbine to spin. The turbine and the compressor are placed on the same shaft, such that when the turbine spins, the compressor will also spin. By burning fuel at a quicker rate, we are able to create more power in the engine, which eventually finds its way down to your tires, propelling you forward. If you’re craving more details on how turbos work, make sure to check out our white paper on the CST4. 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 and K04 compressor comparison

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.

CST6 – The CorkSport Stock Flange Record Turbo

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 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 are 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.  

The compressor wheel utilized on the CST6 the 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 4bar MAP sensor upgrade.  Like the CST5, the compressor housing is a 4inch inlet with anti-surge porting.

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 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 use of the OE oil drain line and all necessary oil feed components and coolant components are included for seamless installation.

Like the CST5 Turbo, we’ve put focus on the wheel size ratio and have validated it’s 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.  

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 quick 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.

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 was validated we moved to design a turbine housing that could provide the necessary boost control and power potential.

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.  

With the use of the EWG turbine housing, boost control is now spot on and can easily controlled 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

Mazda’s Dynamic Pressure Turbo – An Introduction

The SkyActiv 2.5T has been around for a few years in the CX-9 however, things started to get interesting when the engine was dropped in the Mazda 6 for 2018. While lacking a manual and not a true Mazdaspeed, it’s a step in the right direction for the enthusiast. With one of the new Mazda 6s in the CorkSport garage, we’ve been getting curious about where all of that 310lb-ft comes from. Well we decided to call up Mazda and purchase a turbo to see how it all works.

There’s a lot to take in on the turbocharger and there are quite a few things that have changed from the K04 that made its home in the Speeds.

For starters, this turbocharger is pretty big. The wheels themselves are not large, with the compressor wheel very close in size to the old K04 & the turbine wheel only slightly larger than the K04. However, with the dual inlet turbine housing, 90° compressor outlet, and lots of attached electronics, the whole package takes up a lot of room in your engine bay.

The turbine housing is not far from the old K04. A large five-bolt inlet flange has two rectangular inlets to work with the dynamic pressure system (more on that later) and even a port where the EGR system sources its exhaust gases. The outlet is much simpler, using a five-bolt flange to mount to the downpipe, yet does house a surprisingly large wastegate port.

From a performance standpoint, the large wastegate should help eliminate boost creep but the turbine housing will likely need a larger scroll to get some more serious power out of the engine.

The compressor side is packed full of features. As usual, the wastegate actuator bolts to the compressor housing, however, Mazda has switched to an electric actuator. Interestingly, the bypass valve is also electric and is even mounted to the face of the compressor housing.

Some fancy casting design leaves a pathway between the high and low-pressure sides of the compressor and lets the BPV decide when the passage is open or closed. These two electric actuators will mean easy and consistent boost control. The final plastic component on the housing we believe is a boost assisted vacuum source for the vehicle. Finally, the inlet is a typical clamp connection while the outlet uses a 90° turn and two-bolt flange for better accessibility around the wastegate actuator.

With the housings removed, the CHRA of the dynamic pressure turbo is very simple & standard. Oil feed in the top, two-bolt oil drain in the bottom, and standard crossflow engine coolant ports. The compressor wheel is a cast 6×6 unit and turbine wheel is a basic 11 blade unit.

We are looking forward to waking up the Sky-T in the coming months and making the 2018+ MZ6 into something a little closer to a Speed. Stayed tuned, there’s much more fun to be had from the 2.5T!

-Daniel

CorkSport BIG Turbo

Mazdaspeed 3 big turbo upgrade

Good day boosted enthusiast!

We wanted to take some time to give you all a quick update on one of the many projects we have brewing up here at CorkSport Headquarters.

The project I’m referencing, in general, is our 2nd turbocharger upgrade for the Mazdaspeed 3, Mazdaspeed 6 and CX-7. This unit is a substantial upgrade over our current 18G turbocharger. This Turbo will cater to those looking to take their performance and power goals to a higher level.

Not only will it be capable of putting you well into the 465whp range but this CorkSport Turbo upgrade will be able to do it without giving up on reliability and throttle response.  

It will be very beneficial to those who have mildly-built blocks and a supporting fuel system that will allow them to get higher in the HP range.

So, let’s talk about some of the features you can expect on the upgrade and why we decided to utilize them.

 

 

Let’s start at the heart of the Turbocharger.

The new CorkSport turbo will take full use of a GTX3076R center housing and rotating assembly (CHRA). The unit is equipped with a fully sealed ball bearing cartridge, which is a nice upgrade when compared to a standard journal bearing unit. We chose to go with a ball bearing unit for a few reasons.

  1. The enclosed design of a ball bearing system allows us to eliminate the need for a thrust bearing, which can account for about 40% of the bearing system drag on the turbos rotor assembly.
  2. Ball bearings reduce the viscous drag, which allows a ball bearing unit the ability to spool up about 15% faster than its journal bearing equivalent.

The next thing you will notice on the new Mazdaspeed Turbocharger upgrade is the holes that are drilled into the compressor cover. These little holes are known as anti-surge ports and are intended to expand the turbochargers compressor map. The ports function to move the surge line further left on the compressor map which gives the Mazdaspeed turbo some more headroom before it falls out of its efficiency island. Anti-surge ports are becoming increasingly more popular in modern performance turbochargers and with great reason. They offer some unique benefits as mentioned and will be fully integrated into our unit.

 

Last but not least, as with our CorkSport Turbo, this bigger Mazdaspeed Turbo will once-again be a true drop-in unit; minus the 4” compressor inlet.

There will be no cutting, modifying, sourcing oil and coolant lines, running to the store to buy couplers, etc. This unit will come with everything you need to have a trouble-free install. As with the current CorkSport 18G turbocharger, the new Garrett-based design will come with all studs, gaskets, washers, and knowledge that you need to have a nice weekend install.

So keep your eyes peeled as we get closer to delivering more performance for the Mazda community!

– The CorkSport Team

 

SOURCES: Miller, Jay K. Turbo: Real World High-Performance Turbocharger Systems. CarTech, 2008.

 

Mazda Shows Us Some Forced Induction Fun

A recently submitted patent popped up from Mazda, which gives all of us boost lovers a serious case of envy.
PC: _._hay.hay_._

 

 

 

 

 

 

 

 

A recently submitted patent popped up from Mazda, which gives all of us boost lovers a serious case of envy; a motor with 2 turbochargers and a supercharger. Text from the patent reads, “The supercharging device according to the embodiment schematic includes first and second exhaust turbochargers 11 and 15 to be driven by exhaust energy of the engine 1, an electric supercharger 18 to be driven by electrical energy, and intercooler 16 which cools intake air discharged from the first and second exhaust turbochargers 11 and 15 and from the electric supercharger 18, and an intake manifold 10 which communicates between the downstream end of the intercooler 16 in the intake air flow direction and the intake ports 3 of the engine 1.”

A recently submitted patent popped up from Mazda, which gives all of us boost lovers a serious case of envy.

This sounds like a party to me and looking at the pictures and further in the text, this motor is designed to be in a rear wheel drive car. Currently the only rear wheel drive model Mazda offers is the Mx5/Miata. Could we be seeing a future Mazdaspeed hotrod in the making?

A recently submitted patent popped up from Mazda, which gives all of us boost lovers a serious case of envy.

Knowing that the Mazdaspeed name is dead, if this new motor comes to life, it would be under the Skyactiv X name and could explain where the future of the Mazdaspeed name was headed. Mazda says “driving matters” and with the boundaries they are pushing with the internal combustion engine in development, this could be another forward-looking motor to make the retired Mazdaspeed name proud.