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2018+ Mazda6 Performance Exhaust for the 2018-up 2.5T

Mazda did a great job bringing a turbocharged engine back to the Mazda 6 (Mazda 3 next please?), but may have done too good of a job of keeping it quiet. Say hello to the CorkSport 80mm Cat Back Exhaust and Axle Back Exhaust for 2018+ Mazda 6 equipped with the turbocharged 2.5L engine. If you’re interested in waking up your SkyActiv-T in both excitement and power, read on as we breakdown the newest CS exhaust.

As with all CorkSport exhausts, the goal of the Mazda 6 2.5T exhaust is to improve power and sound by improving the flow of the OEM exhaust. We started by increasing the size of the piping from 60mm to 80mm. That is an increase of over three-quarters of an inch to really help your turbocharger breathe better. In addition, the CS exhaust system eliminates the crushed areas present in the OEM exhaust and replaces the restrictive muffler sections with pass-through resonators. These resonators control volume and drone without affecting power output.

All that extra flow does mean a power increase. In our in-house dyno testing, we saw an increase in 5-6WHP just by bolting on the CorkSport  Cat Back Exhaust. Check out the dyno sheet down below to see. This increase came with no tuning changes, no check engine lights, and the only other mod being the CorkSport Short Ram Intake, which was installed for both tests. With the 80mm piping size, this exhaust is ready to support future modifications and would likely show more power gains with proper tuning.

The CorkSport MZ6T exhaust is more than just function. We went through multiple iterations and designs to ensure the best-sounding exhaust for your Mazda 6. The finished product ups the volume without being annoying to daily drive yet still sounds great when in hard acceleration. We strongly recommend you watch the video below to hear what to expect from this exhaust.

If you feel the video below gives you too much volume for the daily, then check out the Axle Back Only Exhaust.  Recently added to the CorkSport line-up, the Axle Back alone adds a mellower, but still noticeable tone to the exhaust.  This is a great middle ground between the CorkSport Cat Back and the stock exhaust.

To give a great-looking, long-lasting finish to each exhaust, they are manufactured from fully polished 304 stainless steel. To ensure a high-quality fitment, all components are precision TIG welded together on jigs made from OEM exhaust components. Lastly, as a finishing touch, we use 100mm dual wall exhaust tips. They fill out the bumper cutouts and are extended slightly to give a classy look and enhance the new Mazda 6’s styling.

The CS Mazda 6 Turbo Exhaust comes with all the hardware and gaskets you need for installation, high quality instructions, and CorkSport support for any questions you may have. Pick up a CorkSport MZ6 2.5T Exhaust today and liven up that daily commute.

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CorkSport CST6

Testing & Validation of the CorkSport CST6

As we get closer and closer to announcing the launch of the new CorkSport Turbo Line-Up we want to share the testing and validation we put our turbos through.  You may not realize it, but we’ve already shared a lot about the CST6 without really saying so, check out Barett’s Built Gen1 Here.  

So we’ve talked a bit about the design intent behind the CST6; defining the wheel sizes, wheel size ratio, and the ball bearing CHRA.   If you’ve seen the teaser listing then you’ve already seen the 633 whp dyno graph, so we’ll look at the data to support it!

The First Look at the CST6 Performance

CorkSport CST6 dyno at 28psi
CST6 running at 28PSI

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First let’s look at the CST6 at a more moderate boost pressure.  Above are the results of back-to-back testing comparing the XS-Power V3 Exhaust Manifold and the upcoming CorkSport Cast Exhaust Manifold.  All dyno runs were performed with the same 28 psi peak pressure tune.

So the exhaust manifold testing is exciting, but it’s not what we’re here to discuss.   What I want you to know is that the CST6 is fully capable of providing mid-500 whp power at 28 psi.   While we have and will continue to push the CST6 to its max ability, the 27-30 psi range has proven to be a sweet and efficient spot for the CST6.

Testing the Limits on the CST6

CorkSport CST6 Dyno Graph running 34psi
CST6 running at 34PSI

Searching for the limits with the current fuel system we can easily push past the 600 whp mark plus some.   The efficiency of the CST6 at this power level is still very strong and the turbo continues to pull through the RPM range.   What really makes the CST6 shine is the power under the curve. This is a BIG turbo and will respond like one, but the loss of early spool is easily compensated for with the abundant power curve and power that carries past 7500 rpm.  

It’s important to note that testing for the CST6 is not finished because we are currently limited by the fuel system on the vehicle.   The current fuel system is OE DI injectors paired with a boost based methanol system flowing 40 gph peak. In the near future, we will continue finding the limits of the CST6 with a true port injection system and Split-Second controller flowing E85.   This will give us headroom for 8000+ rpm and boost levels past 34 psi (let’s see what 40 psi give us!).

Looking at the CST6 Data Log

CorkSport CST6 Data Log
MAF Voltage and Actual AFR of the CST6

This is a datalog form the 633 whp dyno run and was recorded on the chassis dyno.   Because of that, it is not a perfect example of street driving… let me explain why. The dyno dynamics chassis CorkSport uses can control load and thus the rate at which the engine can rev through the RPM range.   In order for us to dyno a vehicle at this power level safely, we need to find the right ramp rate for low RPM and high RPM. The biggest factor this affects is the spool RPM of the turbo.

On the graph I marked ~200 rpm shifted to the left for the boost curve.   On the street, the CST6 spools about 200 rpm sooner due to the higher load on the street vs the dyno.   This puts the CST6 @ 20 psi around 3800-3900 rpm.

Also shown on the graph are MAF voltage and actual AFR.   Both of these are important because they provide real data about how the vehicle is being tuned.

Target AFR is set for 11.76 which is neither rich nor aggressive for this setup.  The slight up and down of the AFR curve from 3500-4000 rpm is due to the very high amount of auxiliary methanol starting to spray along with the DI injectors.

Looking at MAF voltage you can see us get well past 4.50v.  Actually, we are consistently seeing MAF Voltage around 4.65-4.70v using the CorkSport 3.5” Intake which has a true ID of 3.50”.  This is just further validation that the CST6 is flowing enough air to support 600+ whp.

There’s more to come from the new CorkSport turbo lineup so stay tuned for more info on the CST5, CST6, and EWG housings.

-Barett @ CorkSport

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Let’s Get Chilly: CorkSport Intercooler for SkyActiv 2.5T

It’s time to break down our design for the CorkSport Performance Intercooler Upgrade for the Mazda 6 2.5T. We have covered both the OEM intercooler and piping, and our design plan for the upcoming Sky-T intercooler piping upgrade in previous blogs, but today’s focus is the intercooler itself. Intercoolers are a delicate balancing act between size, cooling efficiency, and pressure drop so naturally things can get a little complicated. Buckle up and stay with us, and be sure to drop any questions you may have down below.

Taking a look at the stock intercooler mounted on the Mazda 6 (shown above) shows us quickly where our size constraints lie. With the large crash bar, we cannot go too much larger in height without trimming the crash bar, bumper, or both. However, there is a ton of room for added thickness and better end-tank design that can really help increase the width of the intercooler. The stock intercooler core is 24.5” wide, 5.5” tall, and 2.625” thick. Our plan is to fit a 27” wide, 6” tall, and 3.5” core without any trimming. This sizing combined with a low-pressure drop will be good for 400WHP with no issues! Because the Mazda 6 comes with just around 200WHP from the factory, this sized core provides plenty of room for upgrading down the road without causing excessive boost lag that can occur if an intercooler is simply too big. Check out a prototype CorkSport intercooler mounted on the car below.

Mazda 6 Front Mount Intercooler Installed

Now that size is taken care of, let’s move on to cooling efficiency and pressure drop of the CorkSport intercooler for the SkyActiv 2.5T. These are tied closely together as getting extremely high cooling efficiency usually means high-pressure drop and vice versa. Just so we’re on the same page, cooling efficiency is how well the intercooler cools off the pressurized air that passes through it. So a highly efficient intercooler will be able to bring the boost temperatures down similar to the ambient air temperature. Pressure drop is exactly what it sounds like, a loss in pressure from the inlet to the outlet of the intercooler which can be caused by a number of things: poor end-tank design, too many intercooler fins, or simply poor flow distribution in the intercooler. Too large of a pressure drop means lower boost pressures reaching your engine and/or your turbocharger working harder to achieve the same boost levels.

Mazda 6 Front Mount Intercooler product photo by CorkSport

Pressure drop and cooling efficiency are influenced primarily by two things: fin density and end-tank design. Fin density is basically how many fins the boosted air must pass over when traversing the intercooler. More fins = better cooling efficiency, but also more pressure drop. To choose the best core for the SkyActiv 2.5T we plan to use multiple different fin densities and test each for power, cooling efficiency, and pressure drop. While we can get pretty close based on our work from the CS Mazdaspeed Intercoolers, it’s always best to test and identify the best one for each platform. With this extensive testing, we can reach our goal of improved cooling efficiency, lower pressure drop, more power, and no CELs.

Mazda 6 front mount intercooler back

End-tank design is critical as it determines how the air reaches the core of the intercooler. Sharp bends, poor air distribution, and small inlet/outlet size all adversely affect the performance of the intercooler. To fit the core size we want, we had to do away with the plastic inlet and outlet pipes of the stock intercooler. This was advantageous as it gave us more room to have a smooth-flowing end-tank that distributes air well to all the runners and does away with the sharp corners present in the OEM end-tanks. In addition, we were able to increase the inlet and outlet size of the intercooler to 2.5”. This is a fairly standard size that has shown to work well for the Mazdaspeeds with stock power and without choking flow way up to Barett’s 600+ WHP.

CAD design of the 2.5T SkyActiv Intecooler

Those of you with a keen eye have realized that the connection between the CorkSport front mount intercooler (FMIC) and the OEM Intercooler is not the same. As shown in the CAD rendering above, each intercooler kit will come with the silicone and custom adapters that are needed to work with the OEM piping. If you decide to upgrade to the CS intercooler piping kit, later on, the CorkSport Intercooler for SkyActiv 2.5T will not need to be removed, and you will only need to change some silicone parts.

We will have more info on this kit coming soon, with the next blog covering our testing of the different core designs using a few new toys from AEM Electronics. Be sure to check out the product listing for more info, and to be notified when the intercooler is available. Last but not least, CX-9 Turbo and CX-5 Turbo owners, we are 99% sure this kit will also work on your rides but we plan on validating fitment before release!

-Daniel @ CorkSport

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CST6 | Behind The CorkSport Turbo Design

A few weeks ago we discussed some of the design intent behind the CST5 turbocharger for the Mazdaspeed platform.  Today, we want to follow up with the CST6. The CST5 and the CST6 both were a result of CorkSport’s desire to develop a new stock flange turbocharger that goes beyond the power limits of our FANTASTIC  CST4 Turbo.  

During the development of a higher power stock flange performance turbo, we found that we were asking too much of the CST4 Design.  The result of our efforts is the CST5 Turbo which you can see here and the CST6 Turbo which we are about to dig into.  

In this blog, we’ll dig into the wheel sizing, the CHRA, and some of the challenges we faced in the development and testing stages for the CST6.  

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Compressor Wheel

CST6 Mazdaspeed Turbo

The compressor wheel utilized on the CST6 is well-known and trusted, GEN1 GTX76.  The GTX76 compressor is rated for 64 lb/min and is capable of boost pressures that will require a 4 bar MAP sensor upgrade.  Like the CST5, the compressor housing is a 4-inch inlet with anti-surge porting.

Ball Bearing Design for the Mazdaspeed Turbo

CST6 Turbo Backside

Unlike the CST4 and CST5, the CST6 Mazdaspeed Turbo uses a completely different CHRA and bearing system, and for good reason.  As the turbocharger wheel sizes increase so do the weight and potential boost pressure. This results in higher loads on the wheels, turbine shaft, and bearing system. To increase the durability and performance of the CST6, we opted to move from a conventional journal-bearing design to a more modern and robust ball-bearing design.  

The ball bearing system improves durability and stability for high horsepower/high boost operation along with improved spool and transient response.  Changing the CHRA did pose some new challenges, however. Ease of installation has always been a key feature with CorkSport products and that’s not lost with the CST6.  The CHRA has been modified to support the use of the OE oil drain line and all necessary oil feed components and coolant components are included for seamless installation.

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Turbo Compressor Wheel

CST6 Mazdaspeed Turbo Compressor Wheel

Like the CST5 Turbo, we’ve put a focus on the wheel size ratio and have validated its performance. The CST6 Performance Turbo uses the Gen1 GTX76 compressor wheel paired with the Garrett GT35 turbine wheel…aka GTX3576r.  This wheel combination provides us with a ratio of 1.12 which falls well within the rule of thumb discussed the in the past CST5 blog.

In testing, we found that increasing the size of the turbine wheel from a GT30 to a GT35 with the same GTX76 compressor wheel resulted in more top-end power and no penalty in spool time.  This combo also provided a good power delta from the CST5 to better provide an optimal power option for the community. Since then the CST6 has proven power at 600+whp at ~34-35psi and testing will continue past 40psi.  

External Wastegate

CST6 Turbine Wheel for Mazdaspeed

The initial testing of the CST6 Mazdaspeed turbo started with an internally wastegated turbine housing as that was the original goal with the CST5 and CST6.  However, it quickly became obvious that a turbocharger of this size and power potential could not be safely controlled with an internal wastegate.  The amount the wastegate port and “exhaust” or flow was not nearly adequate for proper boost control.

The boost would creep to nearly 26psi with no signs of tapering off.  Nevertheless, we continue testing knowing that auxiliary fueling was necessary.  Once the CST6 power and durability were validated we moved to design a turbine housing that could provide the necessary boost control and power potential.

Turbo Internal Wastegate Housing

Above is the removed CST6 internally waste-gated housing.  In our testing, we pushed the turbo to nearly 600whp with 40gph of methanol auxiliary fueling.  This amount of heat combined with a turbine housing that was literally being pushed to its limits resulted in a great learning experience.  As you can see, the turbine housing was cracking! The GT35 turbine wheel and power was just too much.

From this discovery and analysis, we developed the EWG turbine housing with the CST6 in mind.  The scroll size was increased, wall thickness increased in critical areas and the 44mm EWG port added.  

CST6 IWG vs EWG

With the use of the EWG turbine housing, boost control is now spot on and can easily control from spring pressure to an excess of 35+psi.  Stick around as we continue to push the limits of the CST6 Mazdaspeed Turbo as we continue testing and validation of the CorkSport V2 Intake Manifold w/Port Injection.  

Thanks for tuning in with CorkSport Mazda Performance.

-Barett @ CS

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Mazda 6 2.5T Stock Spring Evaluation

Today we’re taking another dive into OEM Mazda parts to better understand how they function. Specifically, OEM suspension springs, since there are CorkSport Lowering Springs coming soon for the 2018+ Mazda 6 2.5T. While a simple concept, springs are very important to the handling, appearance, and comfort of your vehicle.

Mazda 6 back side with lowering springs

The new Mazda 6 Turbo uses a lot of the same components as the GEN 3 Mazda 3 and Mazda 6, however, the suspension has been optimized for the new “premium” feel and to deal with the extra weight that comes when adding a turbo. The SkyActiv chassis has primarily remained the same though, with the same MacPherson strut front suspension and multi-link rear suspension shown below.

Mazda 6 suspension diagram

Now, onto the springs themselves; both the front and rear suspension of the Mazda 6 use standard compression springs. The spring’s job is to support the weight of the vehicle when at rest and adsorb impacts when hitting bumps or going quickly around a corner. That’s it. Seems simple enough right? Since the springs are the parts of the suspension that “suspends” the vehicle though, their characteristics and how they interact with the rest of the suspension system are critical.

Lowering springs design by CorkSport for Mazda 6

There are two main characteristics that define a spring: rate and free length. Both are pretty easy to understand. Free length is simply the length of the spring with no weight or force acting on it. So set a spring by itself on a table, measure how tall it is, and there’s your free length.

Spring rate is a little more complex, as it is the measure of how much weight it takes to compress a spring a given distance. So, if you have the same weight and put it on two different springs the one with the higher rate will compress less. The rate is usually measured in kg/mm (often shortened to K) or lbs/in.

For example, if you had a 2K spring and a 4K spring and applied 100kg to each, the 2K would compress 50mm and the 4K would only compress 25mm.

The spring view of the CorkSport Mazda springs

What do these measures mean for your car though? If we keep the rate the same but only change the free length, the shorter the spring, the lower the car. For a given car, a spring can be too short, causing poor ride (sitting on the bump stops all the time), or the risk of a spring coming out of place, causing noises or at worst, the spring falling out of the vehicle.

If we change the spring rate and leave the free length the same, things are a little more complicated. The higher the rate, the stiffer the ride is, plus your ride height will increase. Since the weight of the car is not changing, the higher rate spring will now compress less when the car sits on it, meaning your car sits higher at rest. Too large of a rate and your OEM shocks cannot keep up causing a bouncy ride, and vice-versa if too soft you are hitting bump stops over the smallest bump. Obviously, there is a balancing act to get the spring rate and free length correct for the application for the best in appearance, handling, and comfort.

Mazda 6 2.5L Turbo with lowering springs

Now that the basics are covered, let’s look specifically at the Mazda 6 2.5T. The OEM springs give a good ride as to be expected (likely very soft spring rates) as this can be a huge issue for potential customers if the car ride quality is harsh. Handling is decent overall but has a few quirks. When going around a corner quickly, the car rolls over onto the rear springs excessively before settling and getting through the corner. When at the limit of traction, the car understeers severely, like most cars sold today.

Finally, the ride height is pretty high, likely to prevent any issue with driveways saying hello to the new front fascia. Interestingly, the MZ6T sits a little higher in the rear; we think it ensures enough suspension travel in case there’s a full load of passengers and a full trunk.

Side view of Mazdsa 6 Turbo lowering springs height

For further analysis, we also had the OEM springs tested for rate and ended up with the following: 3.05K front, 5.05K rear. While these numbers are fairly arbitrary right now, they are a necessary data point to have when designing lowering springs. These rates also contradict a very common misconception. Many people think that because there is less weight in the rear of a front-wheel drive car, the spring rates must be softer in the rear for a good ride & handling. This is simply not true in most cases, after all why would Mazda do the opposite? Due to the design of the rear suspension, the spring is basically being pushed on by a lever. This means the spring needs to be stiffer in order to support the same amount of weight as if the lever wasn’t there.

So overall, the OEM springs are good, but have plenty of room for improvement. I just touched the surface of suspension design and as we go through more of this project we’ll get into dampers, natural frequency, and much more. Stay tuned for more info and if you have any questions, don’t be afraid to ask! Check out the release blog for the Mazda 6 lowering springs.

-Daniel @ CorkSport

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