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
We are proud to release the https://corksport.com/2018-mazda-6-2.5l-turbo-boost-tubes.htmlCorkSport 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 install 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!
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
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.
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