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.

3D Printing at CorkSport

You may have seen some funny looking parts floating around on the CS channels that did not look like the typical aluminum or steel parts you install on your Mazda or Mazdaspeed.

These plastic parts are made through 3D printing, a method we use often in R&D to really understand the ins and outs of a part. We’ve been getting a lot of questions lately on our 3D printers so I thought I’d run through what they are, how they work, and what we use them for.

3D printing is quite a simple process even though it may not seem so to start. In normal manufacturing, you start with a block of material and cut away portions until you achieve the shape you want. In 3D printing, you add material (usually plastic) layer by layer until the shape you want is achieved.

For a lot of 3D printers, including both of the CorkSport printers, you can visualize a hot glue gun attached to a robot. The robot controls where the “glue” is extruded and once the first layer is complete, the robot simply moves the object downward slightly and another layer begins. The second layer attaches to the first and you slowly gain height and shape until your part is completed.

This method is uses plastic “filament” as the material fed into the machine. Think of a spool of wire but instead of being made of copper, it’s made out of a recyclable plastic. This material is fed into the machine where it is melted and extruded like the glue in the above analogy. Other 3D printers use liquid resin that is solidified layer by layer or a powder material that gets bonded together layer by layer. The image below shows an almost empty vs brand new filament spool for our large 3D printer. To give you some scale, that is a 4 inch inlet air filter next to them– 10kg is a lot of filament!

We have two printers at CorkSport, a large Gigabot, and a small MakerBot 2X. The Gigabot can print anything that will fit in a 2-foot cube which is more than enough space for the majority of CorkSport parts. The MakerBot is much smaller, only about 9.5” by 6” by 6”. We typically use the Gigabit for most of the R&D testing and the MakerBot for making cool stuff for you all! However, the MakerBot uses a different plastic material that is stronger and more resistant to heat, allowing the parts to be tested on a running Mazda (albeit for a short time).

Barett and I use our 3D printers as tools to aid in R&D. We can take apart directly from a design in SolidWorks to a physical object extremely easily. Once we are happy with a design, it gets saved as a “mesh” made up of hundreds or thousands of tiny triangles. This is imported into a “slicer” program that does just as its name says: slices the part into layers. The part information as well as the settings for the print is exported to an SD card, which we use to upload the information to the printer.

Once we hit “print” all we have to do is wait. Smaller parts like brackets and fittings can be printed in an hour or two while large parts like manifolds or intercooler piping can take multiple days. 3D printers enable us to start a print on a Friday afternoon and leave it like this:

When we show up on Monday, the print is complete, ready for a test fit, and looking like this (Mazdaspeed 6 FMIC Piping):

I can’t express enough how much easier it is to have a physical part to test fit than to try to measure in all of the awkward angles and spaces that exist in a Mazdaspeed engine bay and hope your design will fit.

Having the capability to make a quick and inexpensive prototype to throw on a car can save countless hours and headaches down the road. This is why we use 3D printers so extensively: it makes producing great parts for you all so much easier. Some of our manufacturers even use our 3D prints to help understand the part, help with quoting, and even use them for mold/jig making. At CorkSport, our 3D printers are used almost as much as our 10mm sockets!

I’ve just scratched the surface on 3D printers, their uses, and capabilities so, if you have any questions post it down below!

-Daniel

CorkSport Balance Shaft Delete Kit for 2006-2013 DISI MZR

Looking to add some Extra Excitement to your Mazdaspeed?

What if we told you could add extra engine protection at the same time? Introducing the new CorkSport Balance Shaft Delete Kit for 2007-2013 Mazdaspeed 3, 2006-2007 Mazdaspeed 6, and 2007-2012 Mazda CX-7. It contains all the parts you need to safely remove the OE balance shaft from your MZR DISI engine and give it the extra rev-happiness that it needs.

The OE balance shaft is an 18-pound lump that lives in your oil pan to help balance out the natural vibration and harshness that are inherently present with an inline four-cylinder engine. It does this by connecting to a large gear on your crankshaft and using rotating mass to help cancel out the vibrations from the engine. By removing the balance shaft, your engine has less weight to turn and thus, can change RPM more rapidly. If this sounds familiar, it’s because lightweight flywheels do the same thing; remove some of the rotating mass of the engine to gain a faster revving engine and even a few bonus horsepower.

The OE balance shaft needs an oil supply to ensure that it stays well lubricated and does not lock up. The CorkSport BSD Kit uses a stainless steel plug and O-ring to seal this oil passage. The O-ring is not enough to seal and keep the plug in place, however, it is locked down by a securing plate which gets attached using one of the OE balance shaft mounting holes. We chose stainless for its strength over aluminum. By doing so allowed us to create a lower profile plug with a thicker O-ring for better sealing. We were also very careful to choose an O-ring that is safe for all types of oil and safe up to 400°F.

But you may be asking where does the engine protection come from?

Since the OE balance shaft lives in the oil pan, it takes up some volume that could otherwise be used for oil capacity. This means roughly a quart of extra oil can be used once the BSD kit is installed. Also, the CorkSport Balance Shaft Delete Kit comes with an oil pan baffle to help control your oil’s movement during aggressive driving.

While rapidly changing direction or during a long sweeper at high speed, the oil in your oil pan can move around a surprising amount. If the wrong set of circumstances happen, your engine can be starved of oil, which can easily damage vital engine components. The CorkSport Oil Baffle controls your oil’s movement, ensuring that your engine will have a good supply of oil no matter the driving situation.

We again choose stainless over aluminum for the oil baffle, so that it is rigid enough to control your oil and prevent any vibrations or rattles while your engine is running. The oil baffle is made from two laser cut pieces that are then attached using stainless steel rivets to eliminate any risk of corrosion or improper hole alignment.

Note: the CS BSD Kit comes fully assembled and ready for installation.

Since the CorkSport BSD Kit removes a stock component designed to make the car more comfortable, it will naturally have an increase in noise and vibration coming from the engine compartment. As such, we cannot in good conscience recommend this mod to everyone. That does not mean it is unbearable though, Barett at CorkSport still daily drives his fully mounted Mazdaspeed3 with a CS BSD Kit installed.

If you are looking for the next mod to get some more excitement from your Mazdaspeed, look no further than the CorkSport Balance Shaft Delete Kit. After all, how many mods come with some extra engine health as well?

The First and Only Performance Mazdaspeed Throttle Body with NO Sacrifices

Mazdaspeed3 intake manifold and throttle body installed

The First and Only Performance Mazdaspeed Throttle Body with NO Sacrifices

Many have tried, but few have succeeded to retrofit or modify an existing throttle body to work with the Mazdaspeed DISI MZR platform.

As you know, CorkSport does things a little differently, and as a result, we started from the ground up to create the best performance throttle body possible with no sacrifices to drivability or reliability. Introducing the CorkSport 72mm Throttle Body for 2007-2013 Mazdaspeed 3, 2006-2007 Mazdaspeed 6, and 2007-2012 Mazda CX-7.

Starting from the ground up means 100% brand new parts, no reworked or refurbished components anywhere.  

We start with an aluminum investment cast body that is made to our specific design specifications.

A flat faced throttle plate is added to gain a little bit of extra flow by avoiding the bump of a traditional round pivot shaft.

Finally, new electronics are added that are based upon OE logic to avoid any tuning and calibration issues.

To retain easy installation, we knew we had to keep the OE bolt pattern. With this, we wanted to maximize the throttle plate diameter for maximum flow. We ended up increasing from 60mm to 72mm. This may not sound like a huge increase, but the OE Throttle Body fits inside the CorkSport Throttle Body with plenty of room! The 72mm size also fits well with both 3” and 2.5” intercooler piping to fit almost any TMIC or FMIC setup. Finally, we did away with the OE gasket (which is too small anyway) and replaced it with a durable O-ring that will hold up to oil, gasoline, methanol, and other fueling options that it may come in contact with.


The CorkSport Throttle Body underwent extensive testing to ensure that it will not fail during daily use and to ensure it performs as well as we expect. The throttle plate underwent endurance testing to validate the D-shaped pivot can stand the test of time. During flow bench testing, we found that the CS TB flows about 150CFM (~33%) better than the OE throttle body when 75% open (accelerator pedal fully depressed).

Check out the graph below for the full data.

In daily driving testing, we noticed better throttle response with no CEL or choppiness. In power testing with a midsized turbo (~GT30 size) we found the throttle body caused faster spool, but when we moved to a big turbo, things got interesting. With a GT35R, the CorkSport Throttle Body caused 100-200RPM faster spooling and an increase in power. Check out the dyno graph down below to see the difference between the CS Throttle body (blue) and the OE throttle body (green).

Each throttle body ships with fresh stainless steel mounting hardware, a 3” stainless t-bolt clamp, and your choice of silicone. We have options for FMIC, MS3 TMIC (which also works for you CX-7 guys), and MS6 TMIC.


If you’re looking to take your Mazdaspeed3, Mazdaspeed6, or CX-7 to the next level, or squeeze that last bit of power out of your big turbo build, the CorkSport Throttle Body can help you meet your goals.

Dear Mazda, I have a Wish List

Dear Mazda,

I want to let you know what’s on my wish-list so that if you ever happen to stumble upon our wonderful little world of CorkSport, you’ll see everything I’ve been dreaming of.

1.      New Mazdaspeed

While I personally prefer the Mazdaspeed3 hatchback look, I’d even be ok with a Mazdaspeed6 iteration. I like to have fun; I like to be pushed back in my seat by power and performance, and realistically I LIKE TO GO FAST. The newest generations of Mazda are missing some of these aspects, and I’ve been dreaming of their return!!

Now, don’t get me wrong, I like the Gen3 Mazda3. It’s a smooth ride, and we’re pretty stoked about what it can offer. However, our customers like to make power, N/A leaves us begging for more despite what HP we can squeeze out of the Mazda3.

So, Dear Mazda, Please bring back the Mazdaspeed!

2.      Mazda CX-3 with a turbo

Genuinely, I like the look of the CX3, I enjoy the size of the CX-3 and even find that it suits my ever changing lifestyle being a little higher off the ground. (For those who don’t, check out CorkSport’s lowering springs for the CX-3). It’s just flat out missing the power that comes with a turbo. It’s “get up and go” is … well… slow. This could, with the right improvements, be a great replacement for the Mazdaspeed3 for those of us waiting for the newest generation. Just please, please, can we get some more POWER?!

3.     Turbo Diesel Mazda 6

You gave it to everyone else!!! Why in the world would you leave us out?! You have to do ZERO redesigns; just getting it to the states is all I’m asking. The clean look of the Gen3 Mazda6 is something we like, but the power and improvements that come with the Turbo Diesel, I mean COME ON?! Just let us have a chance at it!

Heck, make that an AWD Mazda 6.

If you’re feeling generous, you could make it an AWD Turbo Diesel Mazda 6.

If we’re going THAT far, make it an AWD Turbo Diesel Mazda 6 wagon, because “I love me some hatchback!” that big booty look, and being able to fit all of the things… What’s not to love?!

It’s not a long list, and I realize that it’s selfish of me to ask, but I’m pretty sure I’m not the only one you would be making happy if you would just deliver on even ONE of these items.

Hopefully yours,

Kim@CorkSport

 

P.S Apple Carplay, and Android Auto… have been in the works for about 3 years, and you probably could have just hired a coder and completed a custom code in half the time… so we’re still waiting for that one too.