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.
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
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.
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
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.
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.
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
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.
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.
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
4 years ago, we released the 60.5mm Exhaust kit for the 3rd Gen Mazda 3 (both in
The Dirty Details
Now I know what you’re thinking, an 80mm exhaust seems excessively large for a naturally aspirated car making less than 200whp. But, hear me out because I think you’ll like what’s coming.
80mm piping allows for some unique & louder tones its smaller little brother can’t offer, but it wasn’t as easy as just using the old design and making the pipes larger. We had to do quite a bit of resonator experimentation and NVH analysis to get to the finished result with as little drone as possible. I’ll be upfront with you guys though, this is loud. It’s a good loud with tons of fun noises, but if you’re looking for something subtler, then our 60.5mm cat back or axle back may be a better fit. We do a good job of capturing the audio for you though so you have a good understanding of what you’re getting. Be sure to check out the product video to hear it.
The Beauty of the Design
For those wanting this more aggressive exhaust note, sound isn’t the only bonus. We thought about the appearance, and how we could take advantage of this time to tinker with the design. The 80mm does a nice job of not only filling the exhaust tunnel under the car, but the axle back portion is a bit more prominent when you catch a glance.
On the Hatchbacks, the exhaust tips got a nice size increase up to 100mm and they are slant cut to help follow the profile of the bumper. Sedans have also been upsized to 100mm tips, which were lowered slightly to ensure your bumper doesn’t melt with the large piping. This has the added bonus of making the tips a little more visible from the rear and side of the car. In both cases, the way the upsized exhaust accents the rear of the car provides an aftermarket look, that’s classy and somehow the way it always should have been from the factory.
As with every CorkSport exhaust, this new 80mm variant is made from fully polished T-304 stainless steel for long lasting corrosion resistance. All flanges, hangers, and resonators are precision TIG welded in place while all of the piping is made with smooth mandrel bends. Each resonator uses a direct flow-thru design to keep the drone down and the volume up without sacrificing power.
Speaking of power, check out the dyno graph below. The upsize to 80mm showed similar power gains as the 60.5mm variant, so the extra size isn’t really needed at similar to stock power levels (aside from the great noise of course!). The only change in parts or tune between the two graphs was the exhaust. OEM exhaust (red) vs. CorkSport 80mm Exhaust (green).
We also believe it’s also very important to be prepared. Future proofing your car for mods down the road is always a great idea, and you’ve probably heard that we have a turbo kit (yes it’s still happening!) and race header in the works. More on those projects later, but I’ll let you put 2 & 2 together…
We recently went over the stock intercooler & piping system for the 2018+ Mazda 6 2.5T. If you missed it, be sure to check out the blog HERE.
Today, it’s the first look at the CorkSport parts that will be coming in the near future to remedy the issues we found with the OEM system. We are not covering our upgraded intercooler just yet though; today’s focus is piping upgrades!
As you can see we’ve been busy getting the upgraded intercooler piping designed & 3D printed for test fitting (while you can’t see it I promise the cold pipe is hanging out in there too!). I’m happy to say there’s plenty of room to fit the upgraded piping sizes that we were targeting and
hopefully they will net us a few HP gain without any other changes.
These horsepower gains typically
comes from removing sharp bends and diameter reductions in the stock piping that cause pressure losses. Then, the turbocharger can operate more efficiently to reach the desired boost level. Now how about some more detail on how and why each pipe has changed.
Starting off with the hot side of things (piping from turbo to intercooler), check out the CAD image above. As you can see, the OEM piping (left) is smaller than the CorkSport piping (right). In fact, we plan to use 2.25” piping for the hot side. Note that the plastic OEM piping is much thicker wall than the CS aluminum piping so even if the outer diameter looks similar, the inside diameter is much larger.
In addition, we keep this same inside diameter throughout while the OEM piping has a major diameter reduction through the middle. For those of you coming from a Mazdaspeed 3, 2.25” is the same size used on the hot side of all CS intercooler kits and has proven itself to support 600+WHP on Barett’s car (more info on that HERE). While we know the Sky-T may
not be to that level just yet, 2.25” is a great size that gets the hot air to the intercooler as fast as possible while retaining high horsepower capabilities.
It’s not all about size though. Instead of using many tight radius direction changes like OEM, the CorkSport hot pipe uses smooth, large radius mandrel bends throughout. This means smoother and faster airflow to your intercooler. Lastly, you may notice the CS hot pipe is significantly longer than the OEM hard plastic unit (the OEM rubber tube starts at the connection point circled in the image above). This reduces the amount of flexible connector used, limiting what could expand at high boost levels. That being said, the CorkSport kit will use high strength silicone with four fabric reinforcement layers to prevent any expansion anyways.
The cold side of the system was already a decent diameter from the factory, but as you can see, we went even larger. The rubber OEM cold pipe will be replaced with a 3” diameter aluminum pipe. This large diameter pipe and huge volume of air that comes with it right before the throttle body has proven to help throttle response and reduce boost lag on our GEN2 Mazdaspeed 3 FMIC kit. We hope to get much of the same from the SkyActiv 2.5T. The cold side also uses large radius mandrel bends for smooth and fast airflow.
Lastly, the cold side piping reduces the amount of flexible connector used. And just like the hot side, each end of the pipe will use 4-ply reinforced silicone to prevent any expansion under high boost levels.
Those of you with a keen eye will have realized that our planned silicone connectors do not use the same connection style as the OEM intercooler. This is for good reason: we believe that the OEM intercooler will run out of cooling capacity before the OEM piping really becomes an issue. So a piping upgrade by itself wouldn’t show too much of a performance advantage.
In addition, we were able to design the piping to be the best it can without using the constraints of the OEM intercooler. So yes, the upcoming CorkSport intercooler upgrade will be required for the CS piping upgrade to work, but it’s so the CS piping & FMIC combo can be the best it can be for you all!
For those of you that have stuck around this long, check out this tease of a CAD model of the CorkSport FMIC & Piping kit.
And just because we like teasing you, check this early prototype out. Testing to come soon!
Stay tuned for more, as next time we will cover the intercooler itself. Also let us know your thoughts down below, we love your input!
-Daniel @ CorkSport