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!

January 29, 2019July 10, 2019

OEM Part Breakdown: 2.5L Skyactiv-G Exhaust Header

Analyzing an OEM part is usually our first step in creating a new performance part. We’ve been looking at the Mazda 2.5l SkyActiv-G Exhaust Header, and I wanted to bring you all along for the ride. It’s surprisingly complex for an OEM manifold/header and some serious engineering went into it.

If you’ve been paying attention to the CorkSport channels, you may have seen rumors here and there of a race header for the GEN3 Mazda 3 and Mazda 6 2.5L. While I can’t say too much on that just yet, but I can give you a breakdown of the OEM exhaust header that’s hiding in the back of your engine bay.

The OEM Exhaust Header

Excuse the dirty part, as this OEM header has had a hard life! I imagine many of you have not seen the stock header as it’s in the back of your engine bay surrounded by heat shields. Taking the heat shields off gives us a glimpse of the craziness that is the stock header. Mazda has gone with a true 4-2-1 design (also known as tri-y) with an integrated catalytic converter and what appears to be equal length runners. Stay with me, I’ll explain what all that means.

SkyActiv-G Exhaust Manifold Flow Path — Exhaust Flow Path

The image above hopefully helps you visualize the 4-2-1 design. Starting at the engine, there are four exhaust ports from the head. Each exhaust port gets its own pipe, known as a “primary”. The primaries then pair together to form two “secondaries”. Finally, the two secondaries combine into one collector pipe, in this case heading directly into the catalytic converter. The three unions or “y’s” are where the tri-y name comes from. The 4-2-1 design was chosen by Mazda for a very specific reason. Check out the image below and Mazda’s explanation HERE.

Mazda SkyActiv-G Exhaust Chart — Residual gas reduction by 4-2-1 exhaust system – From Mazda.com

Essentially, using a very high compression ratio causes very high exhaust gas temperatures. If too much of this exhaust gas is leftover in the cylinders for the next combustion cycle, knocking can occur. In addition, if you have a short 4-1 header or a log-style manifold you can suck exhaust gas into a cylinder before combustion as one cylinder can be on an intake stroke while another is on an exhaust stroke (see the upper image in Mazda’s diagram).

OEM Design Efficiency

The 4-2-1 has two benefits to fight this. First, the long length means the exhaust gas takes longer to traverse the pipes, so one cylinder sucking in another’s exhaust is drastically reduced. Second, the cylinders are paired correctly to one another (1 with 4 and 2 with 3). Since the firing order is 1-3-4-2, each secondary is receiving an exhaust pulse at a regular interval. If you paired 1 with 3 for example, you would receive two pulses quickly, and then a large gap as the other two cylinders fired. This helps with exhaust scavenging as the pulse from one cylinder helps “pull” the leftover exhaust from the cylinder it’s paired with. These benefits can also be present on a long tube 4-1 if designed well but, there is a good reason why Mazda did not choose this option.

Typically a well-designed 4-2-1 will make more power and torque in the midrange while a well-designed 4-1 will make more power way up at the top of the RPM range. Since normal driving does not involve being at the top of the RPM range all the time, it makes sense that Mazda went with the 4-2-1. We will likely do the same as we want to retain the low knock characteristics of the 4-2-1, high midrange power & torque, and because the SkyActive 2.5L is a fairly low revving engine.

It appears that Mazda also went with close to equal length runners. This means that each primary section is the same length and each secondary section is the same length. Having equal length runners ensures the exhaust pulses are arriving at the collector (or Y) at uniform intervals.

The easiest way to explain why this is a good thing is by visualizing the entrance ramp to a highway. When cars entering the highway follow the “zipper” method for merging, the cars currently on the highway do not need to slow down. The highway and entrance ramp merge and flow in a smooth and consistent rate. However, if a surge of cars come down the entrance ramp to merge onto the highway you will get a back-up of cars on the entrance ramp and will disrupt the flow of cars on the highway. If the cars are exhaust gases and the highway is the exhaust pipe, you can understand why equal length can help. Again, we will adopt this strategy with the CorkSport Race Header.

So far so good then, as Mazda has put a lot of thought into making a high-quality stock header. However, as usual, there are a few areas we can improve on. That’s coming in a later blog though so you’ll have to stay tuned for more details! Let us know if you have any questions or thoughts down below.

-Daniel @ CorkSport

January 17, 2019May 31, 2023

SkyActiv 2.5T Cold Side Boost Tube Part 2: Testing

In case you missed it, we have been working on improving the flimsy rubber tube that comes stock on the cold side of your 2018+ Mazda 6 2.5T. Check out the first part on the cold side boost tube here and the full OEM piping & intercooler breakdown here. Since our last installment, we have been busy testing a prototype CorkSport Boost Tube and would like to share some results with you all.

Testing Results

Starting off we tested and data logged both the OEM tube and CorkSport Performance Boost Tube on the dyno. We were not expecting to see too much of a difference to power with just the boost tube changing however, we did see tiny improvements here and there, most notably way up at the top of the RPM range.

Check out the graph below, (OEM: red, CS: green). We tested on the same day in identical conditions and the car had a CorkSport Intake and Cat Back Exhaust installed for both tests.

PLEASE NOTE: the variations below 2800RPM are due to inconsistencies associated with dyno testing an automatic car.

SkyActiv 2.5T Boost Tube Performance Dyno

After noticing these changes, we went to the data logs to see how the boost changed between the OEM tube and the CS Mazda 6 Boost Tube. The graph below shows the engine RPM versus the manifold pressure in psi. Both lines have the same smoothing done to the raw data. As you can see, the CorkSport tube (green) holds about 0.5psi through the midrange (3500-5000RPM) and is almost 1psi more when above 5500RPM. This correlates well with what we saw while dyno testing.

SkyActiv 2.5T Boost Tube Manifold Pressure Test

Testing the Changes

The small increase in boost pressure is likely due to the CorkSport tube not expanding as much when under pressure. To confirm this, we capped off both ends and pressurized each tube to 20psi. Note: do not try this at home as the caps can easily fly off and injure you.

After measuring multiple locations both before and during pressurization, we found that the OEM tube expands about 12% in the internal cross-sectional area while the CorkSport Boost Tube expands 3x less at 4%. Keep in mind that this would be an even larger difference if the same test was performed with the tubes installed on the car due to the heat of the engine bay. Since silicone is more stable than rubber at high temperatures, the heat of the engine bay will not soften it nearly as much as the rubber OEM boost tube. A softer rubber tube would mean even more expansion when pressurized and even more inconsistent boost pressures.

CorkSport and OEM Boost Tube Comparison — CorkSport Boost Tube (left) & OEM Boost Tube (right)

This data may not show drastic changes but it does not tell the whole story. The larger diameter and thus larger volume of boosted air of the CS tube provides a little bit better response when low in the RPM range. While this may just be a placebo effect on our end, there’s not too much of a wait before you can try it yourself! Stay tuned for more information. If you want a more serious upgrade though, keep your eyes out for information on the upcoming CorkSport Front Mount Intercooler kit and Piping Upgrade kit!

P.S. 2016+ Mazda CX-9 owners and future Mazda CX-5 2.5T owners, don’t worry we will be checking this for fitment along with other CS goodies!

-Daniel @ CorkSport

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January 8, 2019August 7, 2023

SkyActiv 2.5T: Let’s Talk Intercooler Pipe Upgrades

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!

Mazda 6 SkyActiv 2.5T engine with Intercooler Pipe

As you can see we’ve been busy getting the Mazda 6 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 gains without any other changes.

These horsepower gains typically come 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.

Modeling and design for FMIC piping upgrade for Mazda 6

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 Mazdsa 6 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 connectors 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 connectors 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 Mazda 6 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.

Mazda 6 Intercooler Pipe Design with FMIC

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

December 6, 2018February 15, 2023

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.

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

The OEM Exhaust Header

OEM Design Efficiency

Testing Results

Testing the Changes

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

Now into the details…

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

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