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
Stock Gen 3 Mazda 3 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.
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.
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.
2.5L Skyactiv-G
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.
OEM Exhaust Header 4-2-1 Design
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
OEM Part Breakdown: 2.5L Skyactiv-G Exhaust Header July 10th, 2019CorkSport
As a car guy, I can appreciate any newly-released automobile despite my individual taste and opinions. I believe every car has its own style, character, and soul, and should be given a chance to win you over.
With that being said, let’s compare the style, character, and soul of two different cars that have found a way into my life this year and see how they measure up against each other.
In one corner of the ring, we have a 2017 Honda Civic Hatchback Sport trim, equipped with a 6-speed manual transmission. In the other corner I have a 2018 Mazda 3 Hatchback Touring trim, equipped with a 6-speed automatic transmission.
I realize these two cars don’t provide a perfect “apples-to-apples” comparison, but I think the differences will make for an interesting comparison, so let’s roll with it.
Exterior Overview:
Walking up to the Civic Hatchback Sport gives me a rush of being a teenager with a new car, as if I was 17 and my dad just gave me the keys to his coveted R34 GTR (maybe that’s pushing it, but you get the idea).
There’s an overwhelming urge to jump in and fast-track the chiseled 4-door to the nearest curvy canyon back road; not to return till the E light brings me back to my senses.
The hard lines, pronounced fenders, and smooth roofline from hood to end of the hatch tell you that the civic hatchback is here to party, but then there’s more. Bump it up to the Sport Trim to add a little attitude with the piano black finishes, grill, hatch spoiler, and matching front/rear lips and side skirts.
Now that I’ve had my teenage fun, it’s time to throw on the button-up and head into town for an eventful evening… with the Mazda 3.
The 2018 Mazda 3 gives me a different feeling than the Civic: the more refined and sophisticated appreciation of being a car guy. I walk up to the Mazda 3 Hatchback smiling; wondering which German exotic I’ll be mistaken for today and knowing that I can enjoy cruising the strip just as much as the autocross course at the local track.
The body lines of the Mazda 3 emphasize the beauty of simplicity: long defining curves, with just a bit of a sharp edge, follow the natural shape of the hatchback from front to rear. The curves tie-in with the front and rear fenders, headlights, and the hood line providing a fluid motion style.
The 3rd Gen Mazda 3 Hatchback does not immediately scream “speed”, but it does whisper “sweet nothings” in your ear. What more could you ask for? However, if you are looking for a little more of an aggressive look, then opt-in for the piano black lip and side skirt kit available from Mazda.
Interior Overview:
Now that we have made it past the sleek curves of the Mazda3, let’s take a seat inside to get a little more up-close and personal.
The first impression of the Mazda3 Touring Model interior is great, to say the least. Strapping in, the black leather seat is plush and supportive with functional but conservative side bolstering. The brushed nickel style accents are purposeful and not overwhelming in the steering wheel, dash, doors, and center console, with the all-black interior broken up with tasteful chocolate/maroon leather in the door panels and center console. Lastly, the beautifully simple exterior curves are brought into the cabin from the door panels and up through the dash. If there wasn’t a large chrome “M” on the steering wheel, I might begin to mistake the Mazda 3 for a more exotic automobile.
Back to the Honda Civic and its more aggressive visual language.
That same language carries into the interior, but in a less-refined manner than the Mazda 3 provides. The Civic’s interior is full of sharp edges, much like the body, and some touches of brushed nickel and carbon fiber print to give it a sporty feel. The seats follow a more functional style with the sports-inspired cloth material, carbon print inlay, and conservative side bolstering. They do the job in creating a sporty look, but leave something to be desired in terms of higher-end quality.
Power:
Both platforms have two engine options, both of which are a naturally-aspirated 2.0L 4-cylinder, producing around 155 hp each. Lucky for me, neither the Honda Civic nor the Mazda 3 have those lowly-base model engines.
The Honda Civic Hatchback Sport comes equipped, standard, with the turbocharged 1.5L 4-cyl, putting down an impressive 180 hp and 177 lb-ft, according to Honda. Most inspiring of all is the spirited 1.5’s ability to produce the torque from a meager 2000 rpm and carry it to 5000 rpm before beginning to fall off. Pair this with the slick 6-speed manual gearbox, and a curb weight of just 2868 lb, and you have a very fun daily driver.
Jumping back in the Mazda 3 Hatchback, we have the 2.5L Sky-Activ G 4-cylinder laying down 184 hp and 185 lb-ft, according to Mazda. The naturally-aspirated 2.5 provides alert throttle response and power that continues to build through the RPM range. The peppy feel of the hatchback could be improved a bit if you opted for the 6-speed manual transmission, unfortunately the automatic takes away from the responsiveness a bit. With similar power, the Mazda Hatchback comes in with a curb weight of 3098 lb for the AT, and 3046 lb for the MT.
Looking at the dynographs, you may notice an issue:
Honda’s claimed crank horsepower and torque match our measured wheel horsepower and torque. Did Honda sandbag their numbers? I can neither confirm nor deny, but we are not the only ones to see this in testing. The Mazda 3 dynograph shows a more typical drop in power and torque to the wheels, as the drivetrain does have some parasitic losses that rob power.
Honda vs Mazda Dynograph | Red = Honda | Green = Mazda
Handling:
Enough about the style and looks, let’s dive into how do these automobiles drive.
Looking at the chassis and suspension, both the Civic and Mazda3 have a 106.3 in wheelbase, 18 in alloy wheels, MacPherson struts up front and multi-link suspension for the rear. Other than the curb weight, we have two very similar vehicles. However, we really start to see differences in the driving experience.
Tossing the Hatchback Sport around corners feels almost effortless; the 5-door is nimble on its feet and eager to respond to every input. The steering is light, bordering on almost numb feeling, but does not show any sign of wandering with inputs. The chassis likes to move around, whether diving into a corner or with body roll through a corner. Despite the moving body, the Civic is predictable and confidence-inspiring. It wants you to rip around low-speed corners with a smile on your face.
Daily driving the Hatchback Sport is also a pleasurable experience; the suspension is not too harsh, perhaps more on the soft side, providing an easy and no-jarring cruise along the interstate. Looking at the lineup Honda has for the Civic this makes sense. The Sport Hatchback stays under the “sport” level of the Civic SI, and if you really want a canyon and track toy, you opt for the Civic Type-R. I do have one major complaint about this model: the clutch engagement is really… disappointing. Tighten this up, and provide a bit more feedback and you can have a real winner.
Now, how does the Mazda 3 hatch stack up against the Honda?
Driving the Mazda 3 again inspires confidence with it’s tidy and playful response to steering inputs, however the steering feels a bit heavier than that of the Civic. The steering provides a bit more feedback and a desired amount of effort; it reminds you that you are driving a full size car instead of a go-kart. The Mazda3 really comes alive through the corners, and you begin to understand why the ride quality has just a bit of stiffness for a daily commuter. The “3” dives into corners with great steadiness, then plants and pulls through the apex. However, the extra 230 lb can be felt, as the car just feels like it’s trying to move more weight around vs the Civic.
For the daily routine, the Mazda 3 hatchback is a joy to drive through the city or on road trips. The slightly-stiff suspension reminds you that the Mazda is willing at any moment to kick it down a gear and have fun, but is still refined enough to sit back and relax. The only criticism I can really comment on is that it feels like the Mazda 3 is really trying to be a “jack of all trades”, unlike the Civic Hatchback Sport. Perhaps, if Mazda brought back the Mazdaspeed or equivalent to the lineup, they would be able to offer more specific performance setups for customers to truly choose what they want, leaving the base Mazda 3 to be a little softer.
Coming back to my earlier sentiment: every car has a style, character, and soul that should be given a chance to be appreciated by any gearhead. Both the Honda Civic and the Mazda 3 have loads of each and love to show it.
When faced with the decision to choose between the two, it’s a difficult choice.
I’m a performance-oriented car guy and I love the fact that the Honda now has a turbo engine in the line-up, so that’s a huge selling factor for me, as well as the boy-racer in me who jumps to put pedal-to-floor every time I look at it. The Mazda 3 Hatch reminds me that I could have my cake and eat most of it too. The exterior is still edgy enough to keep me hooked as a speed-fiend, and the interior is just great, far above what you would expect at the $20k to $23k price point.
As if it wasn’t obvious, we have a plethora of vehicles to work with around here. True to fashion of course, we at CorkSport have gone and done it again: We went and filled some of the last remaining shop space with ANOTHER CAR.
Not just any car. Say “Hello” to our newest addition: 2018 Mazda 3 Hatchback, touring 2.5L SKYACTIVE-G. Equipped with an automatic transmission and some of the nicer creature comforts.
We love the sparkle of the Eternal Blue Mica and of course her 18” gunmetal dancing shoes. However, as with all things good and standard in the world, we couldn’t help but think that the potential for upgrading is endless.
Do we strip it and go full race car? Perhaps something crazy and AWD swap of sorts? Or maybe we take it way out of left field and go rally-style with it?
With the opportunities being endless, it was starting to make our heads hurt, so we decided to take a step back and start with the basics. We asked ourselves:
“How would our average customer who just picked this car up dream of modifying it?”
And that is exactly what we are doing.
If you guys are anything like us, then you have several hobbies that extend beyond just cars. Some of our team’s personal favorite other hobbies include hiking, camping, traveling, water sports, chilling at the beach, and has recently included obstacle course racing. With all these interests taking up different aspects of our time, we would need a ride that can accommodate our lifestyle. While it would be awesome to have a 6-second drag car, we’d probably have to lose some creature comforts or find a pot of gold to cover the cost, and that’s just not what the average Mazda enthusiast is about.
This project, like we said, is for YOU. And if it’s for you, then we need your help in putting it together.
PIC: NWAPA – Vinnie Nguyen
This car, or as we are designating it: “Project CBR” (CorkSport branded ride), will be built by the people for the people.
We are going to take you with us on the full journey of this car; from the basic mods to the full on weekend task. From the daily driver to the long road hauler. From the car wash to the full service details. We are going to show you everything and anything on this car.
And through the whole process, everything is going to be built with your help.
Over the next several months as we put some miles on our test mule, we will want your guys’ feedback.
Do we put springs and shocks on it or full coilovers?
What type of wheels should we get?
Tint the windows, wrap it, get rid of the chrome?
The list goes on!
Every couple of weeks, we will keep you updated on where the car stands and what you think we should do next.
We will create a section on the CorkSport site so you can follow along, ask questions, provide suggestions, and fully immerse yourself into the car. Ever so often, we will also host a poll and you guys will vote on what happens next!
Think reverse sponsored: Instead of CorkSport’s name being the only one on this ride, we will be giving Sponsorship Cred to the Mazda Enthusiasts who give us the ideas for our mods. (first come, first credits).
We’ll put YOUR NAME on the CorkSport Branded Ride.
If you have a Dream Mod, and We pull it off on the CBR, you’ll get the credits… Remember: The CBR is By the People, For the People!
Stay Tuned, we’ll need your feedback soon!
CorkSport
We want YOU to help us design the next CorkSport Branded Ride! September 22nd, 2017CorkSport
Not too often do you get a chance to cage up your family sedan and “run what you brung,” but that’s exactly what Mazda and Robert Davis Racing (RDR) did in the 2013 NASA 25 Hours of Thunderhill. Mazda took three brand new Mazda 6 Skyactiv diesel sedans out to the track and ran them. There were a few on-track incidents in the 2013 race but nothing too serious. Mazda was lining up to run the cars again in 2014, and several things fell into place that allowed CorkSport to provide some additional power improvements to the cars. We outfitted them with a downpipe and exhaust made from 80mm stainless steel, a high flow intake system, an upgraded intercooler and piping, and some ECU tuning. This gave the cars more power to stand a shot at the podium in E1 with better fuel economy than the other class cars and more power than the previous year.
Inside the group of three Mazda Sedans was a rivalry of the Mazdaspeed Guys (comprised of Mazdaspeed Motorsports employees) and the Dealers CEB (Crayon Eating Bastards), a group of Mazda dealership owners/employees. The dealers controlled cars #55 and #56, and the Factory Guys (Mazda Employees) had #70, all fighting it out for bragging rights. Before the race got going #70 hit a snag where a coolant line came loose and overheated a motor, which prompted a Thursday motor change.
By Friday the cars were all in good shape for qualifying. This went down trouble-free despite a giant rainstorm, as if it wasn’t hard enough trying to run a fast lap with 58 other cars out on the track in six classes— all of which had different speeds.
Thankfully, by Saturday morning the weather had cleared up, and the forecast predicted dry racing for the full 25 hours. This prompted us to get the three cars ready to run on slicks which were mounted up on the wheels and installed on the cars.
Right at 11 am the flag dropped and started the longest race in North America. This was, needless to say, an adventure for the whole team. Several hours into the race, the driver of #70 reported that the car would not shift into all of the gears. It turns out the extra power was a little harder on the drive train in the higher gears, which removed the 5th gear from being functional. The driver decided to stay out and run the race in 6th gear until the fuel stop came up. That turned out to be hours later courtesy of the excellent fuel economy of the Skyactiv engine. The pit area was prepped for a transmission swap with a spare gearbox the team had brought with them. Unfortunately, this took the car out of any chance of being on the podium, but with endurance racing you never know what will happen! So the transmission change went ahead as planned.
At the first extended yellow flag session #55 and #56 reported a power loss in the cars. This resulted in a massive jam session to diagnose and fix what was going on with the cars. Since these specific cars live their lives on the track they did not get a chance to be tested with the new modifications at low speeds (AKA street driving speeds) which brought up an exciting challenge with the fire control systems in the cars. It took ~about 2 hours to sort out the problem, and we had the #55 and #56 back at full speed heading into the night.
The #70 was getting its final work completed with the transmission change and ready to head out onto the track again well behind the Mazda dealers in the #55 and #56 cars. Late into the night, after a driver change, we got a call in on the radio #55 had an on-track incident with another car in the E2 class, and sadly both cars had to retire from the race. This E2 class car happened to be leading the class which RDR was also fielding “Kermit,” the green RX8, in. Though the incident was unfortunate, as a result Kermit moved to the leader position of the E2 class.
Several hours later we got a call in from #56 of an off-track situation which required the car to retire from the race too. This put the #70 Mazda 6 in position to finish ahead of the #55 and #56 for total laps if its drivers could finish the race trouble-free. As the sun came up, the #70 car was running without a hitch, as was Kermit.
From sunrise until noon, the race for the two remaining cars was uneventful. At the noon finale of the race Kermit secured the win in E2 for the first time! Like in any race, there were things you learn and adjustments for the next time on the track. I want to give a huge thanks to RDR, Mazda, Mazdaspeed, the volunteer crew peeps , and Weldon for the guidance on my first time being a crew chief for an endurance race. Lastly, a big thanks to Ruandy from Pacific Northwest Life for the great camera shots—and to my family for letting me miss an entire weekend at another race.
-Derrick
Interested in any of the diesel performance parts we developed? Shoot an email to sa***@co*******.com
for more information.
So You Want to Go Racing in a Family Sedan? March 16th, 2021CorkSport
You had questions, we had answers. Here are the top 7 questions we found on Facebook, Instagram, and Twitter:
Question: What would be involved/required for CS to develop injectors for the MS3/6?
Questioner: Vincent Pham
Answer: Fuel injectors, especially direct injection, are complicated high-precision electromechanical devices. A project like this is outside the “normal range” for a small company like CorkSport; therefore, we would have to team up with an injector manufacturer like Bosch to tackle this project. We would also need lots of money. Even with these huge hurdles to overcome, we are investigating the project.
Question: What’s the most power you have seen a SkyActiv-G engine put down?
Questioner: Shane Foster
Answer: I haven’t heard of any high-power SkyActiv-G, and we probably won’t know for some time, unfortunately. Currently, the 2.5L SkyActiv-G engine produces 165hp at the crank, which is nothing to brag about in a market full of 300hp turbo 4-cylinders and 600hp V8s. Although the SkyActiv engines do have something to brag about, they are some of the most technologically advanced engines on the market. With a 14:1 compression ratio, direct injection, and variable valve timing that’s designed to run on 87 octane fuel, there is huge potential for power. CorkSport has an eye on this potential. For more in-depth information, check out the link below.
Question: Best way to clean carbon on the direct injected cars without pulling manifold and media blasting them?
Questioner: Alex Gonzalez
Answer: From my research and personal knowledge, everybody has their own method for better or for worse. One method is to use a ½” diameter hose attached to a shop vac and scrap away, but I don’t recommend that. Another method is to use the PCV port on the intake manifold to slowly suck Seafoam into the intake runners, but again I can’t say I recommend it. You can’t control how much or which ports it goes through and the idea of running something other than gasoline through the combustion chamber bothers me. Ultimately, you should remove the intake manifold and then clean it with a heavy-duty foaming engine cleaner. This will also give you a chance to inspect the intake valve and I do recommend purchasing an EGR delete kit.
Question: What oil should I use in my speed?
Questioner: Alex Duran
Answer: Alex, you really want to stir that pot? O-well, let’s give it a shot. I personally run Mobil-1 Full Synthetic and half a quart of Lucas Oil Stabilizer for 3000 miles. I’m not going to recommend a specific oil, but I will say this. You should run a full synthetic oil and quality oil filter. The oil should be SAE certified and have the manufacturer’s suggested viscosity or be slightly thicker. I say slightly thicker because I have found good results when doing so with higher-than-factory horsepower setups and in severely worn engines.
Question: Think you guys will ever offer full performance engines and components. I.E. big valve head, billet cranks, high comp pistons, or a 2.5 bored to 2.7 with all that plus cams?
Questioner: Colt Krahwinkel
Answer: I’m going to assume this question is directed to all recent Mazda engines for the sake of variety. Unfortunately, we have no plans for the naturally aspirated SkyActiv-G engines other than bolt-ons; there just isn’t a big enough market for that investment. As for the DISI MZR engine, we have produced camshafts and plan to re-release those in the future. Other bolt on’s are either already done or planned, maybe even a turbo, but we don’t plan to get into the engine internals.
Question: How well might breathing mods affect power on the Mazda 2? Say CorkSport SRI, Headers, and CorkSport exhaust?
Questioner: Mike Wildt
Answer: With the combination of those, the highest gain I would expect on a Mazda 2 is 20hp. The exhaust manifold would show the biggest gains, followed by the SRI. The exhaust system will give marginal gains, but a little grumble is always nice.
Question: Why do you highly recommend resonated over straight pipe? (Referring to the Gen2 Mazdaspeed 3).
Questioner: Phil Young
Answer: This can be a very biased opinion and is probably the most highly debated subject among all automotive enthusiasts. Despite that, I will try to throw in some facts. Personally, I can’t stand an exhaust system with an excessive drone. If you can barely hear your passenger, then what’s the point, right? That’s why resonators are important and why I should define the difference between resonators and mufflers. Resonators are typically canisters with strait-through design and perforated tube and packing material. Mufflers generally are canisters with chambers and baffles that divert flow. The resonator does not reduce the grumble of the exhaust that we love; it targets specific frequencies that cause the annoying drone. Mufflers are the opposite. Also, we have had many customers order the strait pipe exhaust system to return it for the resonated exhaust later.
Thank you for your questions, and keep them coming. We’ll have a Q&A every month for your Mazda performance questions.
