Category: Part of the Week

Sometimes some products get lost in out huge catalog of Mazda performance parts. We highlight the best we offer and give more insight into the design and benefits.

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Inside look: CorkSport Mazdaspeed 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 internal wastegate 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 Mazdaspeed Turbo Billet Compressor
CST5 Billet Compressor

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

CST5 Wheel Design

CST5 Turbine for the Mazdaspeed turbo
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 Mazdaspeed Turbo. 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 Mazdaspeed Turbo
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.

Mazdaspeed Turbo Inducer & Exducer

Inducer & Exducer Comparison for the Mazdaspeed turbo and K04
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.  

Size Matters in the Mazdaspeed Turbo

Mazdaspeed CST5 turbo 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 turbo for the Mazdaspeed

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 Turbo 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

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CorkSport Mazda6 2.5T Boost Tube

We are proud to release the CorkSport Upgraded Boost Tube for 2018+ Mazda 6 2.5T and 2016+ CX-9 2.5T. The CorkSport boost tube is larger, stronger, more reliable, and of course better looking than the OEM rubber tube. Increase throttle response down low, hit boost targets easier and future-proof your ride for mods down the road with a simple 1-hour install. Read on for full details and be sure to check out the R&D blogs here and here for the backstory.

In case you haven’t read the previous blog installments, the CorkSport Boost Tube improves on the OEM boost tube by first strengthening the tube. Instead of using rubber with one reinforcement layer, the CS boost tube use silicone with 5 layers of reinforcement. Aside from the extra layers of reinforcement, silicone stays strong at high engine bay temperatures that may cause rubber to flex excessively. In addition, silicone lasts longer and will better resist cracking as your Mazda 6 Turbo ages. The OEM boost tube is made from materials very similar to the OEM Mazdaspeed 3 boost tubes that showed signs from aging extremely quickly, especially when subjected to higher than OEM boost levels. Cracking or splitting of the OEM tubes results in boost leaks and a poorly running car, definitely not what you want from your brand new SkyActiv 2.5T.

The added strength prevents the CorkSport Upgraded Boost Tube from expanding excessively when subjected to pressure. When pressure tested at 20psi (the largest pressure we have seen at the intercooler outlet), the OEM tube was shown to expand 12% at the internal cross-sectional area. The CS tube tested under the same conditions expanded 3x LESS. This difference would get even larger when subjected to the same pressure at a higher temperature. What does this mean for performance though? When you get on the gas, the boosted air will have to expand the tube before it can enter your engine. The less the tube expands, the easier it is to hit boost targets, and the better throttle response you have, especially down low in the RPM range.

The CS Boost Tube also is a larger inside diameter than your OEM tube. It is 3” through the middle vs. the OEM ~2.44”. Since this area of the charge piping system is directly ahead of the throttle body, this large volume of air has the same effect as it does with our GEN2 Mazdaspeed3 FMIC kit, reducing boost lag and increasing throttle response. For full info on why this happens, check out the release blog for that kit here. As a basic overview, the large volume of air right before the throttle body fools the engine into thinking it has a larger intake manifold plenum than it really does. While not as severe of an effect with just changing this boost tube, try it for yourself and see what you think!

Installing the boost tube is a little tricky due to where it is located, but we include high-quality installation instructions to make it easier. Even so, it can be installed in an hour or less in most cases. We also include polished stainless steel T-bolt clamps to ensure a complete seal and add a subtle visual boost.

Be sure to check out the product listing for more pictures, the installation instructions, and a detailed product video. Let us know if you have any questions, we’ll be sure to help you any way we can!


Lastly, if any of you are looking for a more serious upgrade, stay patient, our FMIC upgrade & full piping upgrade kit are coming soon!

Stay up-to-date on the latest news and product updates from CorkSport.

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Best Mazdaspeed Turbo Upgrades – 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 indeed be.

The Best 400 WHP for the Mazdaspeed  

The original “CS Turbo” is now the CST4 Mazdaspeed Turbo to follow the turbo line-up. It is the best turbo used to upgrade the OEM K04 Mazdaspeed Turbo. The CST4 took a fresh approach to “big turbo” with all the included hardware, gaskets, and, direct drop-in fitment.  It removed the guesswork 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.  We think it’s best for Mazdaspeed turbo to get started.

Best Mazdaspeed 3 Turbo K04 Upgrade for 400 WHP
Best Mazdaspeed 3 Turbo K04 Upgrade for 400 WHP

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 making it one of the best turbos on the market.  You will now have an 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.  

Best 500+ WHP Mazdaspeed Turbo

We present to you the CST5

CST5 is the Best 500+ WHP Mazdaspeed 3 Turbo

The CST5 Turbo bridges the gap between drop-in performance and Mazdaspeed’s 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 4-inch anti-surge compressor inlet which will require an up-sized intake system.

Unlike the CST6, the CST5 turbo will be offered in internally waste-gated and externally waste-gated setups.  This provides you with the flexibility to set up 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. This has been the best turbo to achieve 500 WHP.

The Best 600+ WHP Mazdaspeed Turbo

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

Image: Mazdaspeed-6-big-turbo

Best Mazdaspeed 3 Turbo for 600 WHP

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 outpowers the CST4 & CST5, but that’s the point remember?  

The Mazdaspeed CST6 Turbo is a legit big turbo. The spool will be later, but still below 3900rpm for the full boost! However, a turbo setup is not intended for low-end response.  If top-end power is your goal, the CST6 is the best turbo for your Mazaspeed and 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.

Best Mazdaspeed 3 EWG For Turbos CST4, CST5, and CST6

In the coming months, we will share more information about the CorkSport Turbo Line-Up; the design, the testing, and validation of each.  Check out these pages for more information about the Mazdaspeed CST5 Turbo & CST6 Turbo along with the new EWG turbine housing option. Get and boost on!

Thanks for tuning in with CorkSport Mazda Performance.

-Barett @ CS

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MZR DISI Injector Seals – The Correct Seal for YOUR Speed

Many years ago we helped bring a revolutionary design to the Mazdaspeed community.  Fast forward 4+ years and you’ll find that the CorkSport Tokay Injector Seals are still the best option for your Mazdaspeed.  

Recently, we had a customer ship their stock block engine core to us for a fresh Dankai 2 Built Block.  During the engine core tear-down and inspection, we found a set of CorkSport Injector Seals installed.  We realized this was a great opportunity to share what we found with the community.

When the CorkSport Injector Seals arrive at your door they look like this:

Brand new a fresh of the lathe with all of their beryllium copper brilliance.  After many thousands of miles of use and abuse they look like this:

Now to the untrained eye you may think they look bad, but the truth is they look fantastic!  The visible top of the seal has a small amount of carbon deposits present. This is to be expected because this surface is exposed to the combustion chamber.  Moving to the side of the seal you can see a distinct clean edge and no carbon deposits on the sides of the seal. This distinct clean edge is where the exterior of the seal is designed to seal in the cylinder head.  This is awesome!

Now let’s look at the inside of the used seals:

Again we see carbon deposits, but they are in and only in the expected locations.  Moving up the side of the seal you can see a “shelf” or “step” that is clean. This is the edge that the fuel injector seals against. Beyond that the inside of the seal is clean.

From this inspection we can see that the injector seal was functioning as designed and doing its job effectively.  

So you might be asking…”What is so special about this design?” Well, we wrote a two-part design blog answering that exactly.  We highly suggest spending the 10 minutes to read these.

Injector Seals Design Part 1

Injector Seals Design Part 2

This is exactly why every single CorkSport Dankai Built Long Block includes a set of CS Injector Seals, but if you’re not looking for a built block but still want the assurance of the CS Seals you can check them out right here.  The install of the seal can be a bit tricky sometimes, especially getting dirty injectors out of the cylinder head.  Because of that we’ve developed an injector puller tool that makes the job MUCH easier.  

We hope you enjoyed this quick tech inspection of the injector seals!  Thanks for tuning in with CorkSport Mazda Performance.

-Barett @ CS

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2018+ Mazda 6 2.5T OEM Intercooler & Piping Analysis

We’ve already mentioned briefly that we have an upgraded intercooler kit in the works for the SkyActiv 2.5T, but now it’s officially time to dive in and get into how and why a Mazda 6 upgraded intercooler kit is a good fit. To understand how to make a performance part, we first have to understand what makes the stock parts tick and where we can improve them, which is what we will be covering today!

For those of you that are new to the boosted lifestyle, I feel that I should go over a few terms that will be thrown around frequently later in this blog.

  • Hot Side Piping: Also known as just “hot side” or “hot pipes” this piping section carries the pressurized air (boost!) from the turbocharger to the intercooler. As it is before the intercooler, the air has not been cooled and the “hot” name is quite accurate (think 200-250°F. or even more on a turbo that’s too small). Shown above on the right side.

  • Intercooler: A basic heat exchanger. Air flows through the inside and is cooled by air flowing through the outside while you drive down the road. The same way a radiator works except with air inside instead of coolant. It is made up of three parts the “end tanks” and the “core”. The end tanks are what transfer the air from the piping to the core while the core is the actual heat exchanging portion. Shown front and center in the above image.

  • Cold Side Piping: Also known as just “cold side” or “cold pipes” this piping section carries the pressurized air from the intercooler to the engine. As it is after the intercooler, the air has been cooled to make more power. Shown above on the left side.

Now into the details…

The hot side piping must make its way all the way from the rear of the engine to the front of the car. The OEM piping takes a pretty direct route, and is a decent diameter for stock piping, starting & finishing at just under 2” inner diameter. This, however, is where the good things end.

To start, the two rubber sections of the hot side are single ply. These allow for good flexibility on install and to allow for engine movement but will start to expand on higher than stock boost levels, increasing boost lag and decreasing throttle response. In the image above, the main rubber section squishes under the small weight of the upper plastic section of the hot pipe. This isn’t even the main issue with the hot side piping!

The upper plastic section of the hot side has quite a few small radius bends, and a few areas where the pipe reduces in diameter severely, affecting the maximum flow and restricting the power of your 2.5T. Check out the worst area below, it’s tiny!

And what might be causing this reduction in diameter you may ask?


That’s right, its clearance for a hose clamp. Mazda, I’ve got to call you out on this one, couldn’t you have just rotated the clamp, and kept the diameter in the pipe? Anyways, on to the intercooler itself.  

The intercooler itself isn’t too bad, a decent sized core with lots of fins to help cool as good as it can. That being said, there’s still plenty of room for improvements. First: make it bigger. The intercooler mounting could’ve been simplified to get more width, and there’s a bunch of room to go thicker. While thick is not the best for heat transfer efficiency, it will still help cool off the air better. Height is already more or less maxed out without cutting up the crash beam, but we should be able to make enough extra volume elsewhere to make a big difference.

Intercoolers are a delicate balancing act between cooling efficiency and pressure drop. Cores that cool extremely well usually have a larger pressure drop (loss of pressure from inlet to outlet) and vice versa. With the high fin density of the OEM intercooler, we can expect a relatively high-pressure drop (2-4psi would be my rough guess) but pretty good cooling. From early dyno testing on the CorkSport Short Ram Intake, the intercooler does a good job cooling but loses power on back to back dyno runs. I expect that this is the intercooler “heat soaking”. Heatsoak is what happens when an intercooler is undersized or is not getting enough airflow, it heats up and is no longer able to cool the boost off, robbing you of power.

The two images above show the real Achilles heel of the OEM intercooler and what is likely causing the heatsoak issues: the end tank design. Since the charge air enters and exits the core at an upward angle, it’s being directed away from the lower runners of the core. There is a sharp angle that would be hard for the air to turn, meaning the bottom three internal runners (shown with the red box) are likely not actually doing much. So you’ve got intercooler taking up space that is likely not doing much… We aim to fix this.

The cold side of the system is actually pretty good-inner diameter of just under 2.25” on the ends (even larger in the middle) and a short path into the throttle body. We’ve already covered the basics of it when discussing the upcoming CorkSport boost tube HERE. Like with the hot side, the rubber connector is prone to expansion under increased boost levels. While the CorkSport silicone boost tube will still be coming on its own, we plan to offer something even stiffer that is optimized for our upgraded Mazda 6 Front Mount Intercooler kit.

Much more information to come in following blogs as we’ve been busy working away on this project. Stay tuned for full details on the upcoming CorkSport FMIC kit, and if you’ve got any questions, leave them down below.

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