Inside look: CorkSport 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 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.

CST5 Billet Compressor
CST5 Billet Compressor

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

CST5 Turbine
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. 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
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.

Inducer & Exducer

Inducer & Exducer Comparison
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.  

Sizing

CST5 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

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

600hp Mazdaspeed Build Path – CorkSport Barett’s 2009 Mazdaspeed

If you haven’t heard already, the CorkSport Dyno Day and Summer Event was a blast with food, friends, raffles, a Show-N-Shine, and the continuous string of dyno runs.  The highlight of the dyno runs came when one of the CorkSport Engineers, Barett, put his car on the rollers.  With a few minutes of warm up and anticipation building, it was finally time to see what the “CorkSport Speed” could do. 

Getting past the ecstatic crowd to see the dyno screen showed an impressive 620whp/530wtq.  Now, whether you were at the show or not, you may be wondering what Barett’s setup is to support these numbers.  It’s not a short list but is simpler than you would expect. 

In this blog, we are going to layout the WHOLE build to show you how your Mazdaspeed can make 600+whp.  

The engine was built by CorkSport in preparation for setting up the Dankai Engine ProgramIt features Manley Connecting Rods and Platinum Pistons, head work very similar to the Dankai 2 Built Longblock, along with the CS BSD (balance shaft delete) and CorkSport Camshafts.  Holding the block together are L19 head studs and ARP 2000 main studs.  

To get the air in and out of the engine efficiently we have an assortment of bolt-on parts and some prototype parts because what kind of CorkSport R&D car wouldn’t have some prototype performance parts on it?  To break this down in the simplest way possible we have laid out a full build list:

600hp Mazdaspeed Build List:

  • CorkSport Built Engine:
    • Manley Pistons – 0.5mm overbore @ 88mm
    • Manley H-Beam Connecting Rods
    • CS Balance Shaft Delete
    • Dankai 2” Ported Headed: Single Runner Intake, Bowl Work, Combustion Chamber Touch Up, Exhaust Porting
    • CS Camshafts
    • Stock Valve Springs (We would recommend upgrading these and plan to do so ourselves)

Now, this isn’t the complete list, but it does lay out most of the essential parts to get your Mazdaspeed over 600whp.  You might have picked out a couple “prototype” mentions in that list above…well we can share a bit on the new CorkSport Turbo.  You’ve seen the power it can make…and it still has some more left in it up top, now check it out some sexy billet and massive turbine.

Lastly, none of this power would be possible without the fuel to support.  As you may know already, the OE direct injection fuel system taps out around 380whp on an efficient build so how do we make another 240whp?  Auxiliary fueling is the key my friends, and we recently posted a blog to help you explore Methanol Auxiliary Fueling that I invite you to read.  To stay focused on Barett’s 600+whp build we have made an auxiliary fueling build list below:

 

Methanol Auxiliary Fueling 600hp Mazdaspeed Build List:

  • AEM Boost Based Pump Controller
  • Snow Performance 5 Gallon Cell Trunk Mounted w/CS Prototype Mounting Bracket
  • AEM 80 micron in-line filter pre-pump
  • ProMeth 220psi Pump (Essential for flowing this volume of methanol)
  • Snow Performance Solenoid
  • Devil’s Own 1in/4out distribution block
  • 4x Devil’s Own 90degree nozzle holders
  • 4x ProMeth Compact Check Valves (Essential for proper AFR control between shifts)
  • 4x Devil’s Own D07 Nozzles (One per intake manifold runner; each flowing ~10gph)

Despite that this auxiliary fuel setup is providing the fuel required to support just over 600whp; it is at the ragged edge of what can be supported.  Looking at the dyno graph further up you can see torque decline after 6000rpm and horsepower go flat. This is due to the auxiliary fuel system reaching its maximum fueling capacity and thus forcing us to reduce boost pressure as engine RPM goes past 6000rpm.  

At this power level, true port injection auxiliary fueling is the correct step to take.  Lucky for you guys and gals, we are currently exploring this path with our product R&D. We plan to give you guys and gals a full breakdown of our experience and how we built a full port injection auxiliary fuel system that can support over 600whp.  

AND…I forgot to mention one very critical aspect of this entire build.  Professional Tuning! This specific build was E-Tuned on the CorkSport in-house dyno by Dale Owen of Gem Tuning.  E-Tuning is a great way to set up your car with the tuner that is the best suited for your platform and vehicle build because it doesn’t require the tuner and the vehicle to be in the same place at the same time.  

Hang tight for more on the PI Auxiliary Fueling and thanks for tuning in with CorkSport Performance.

-Barett @ CS