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

Stock Gen 3 Mazda 3 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.

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.


2.5L Skyactiv-G
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
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

Mazda’s Dynamic Pressure Turbo – An Introduction

The SkyActiv 2.5T has been around for a few years in the CX-9 however, things started to get interesting when the engine was dropped in the Mazda 6 for 2018. While lacking a manual and not a true Mazdaspeed, it’s a step in the right direction for the enthusiast. With one of the new Mazda 6s in the CorkSport garage, we’ve been getting curious about where all of that 310lb-ft comes from. Well we decided to call up Mazda and purchase a turbo to see how it all works.

There’s a lot to take in on the turbocharger and there are quite a few things that have changed from the K04 that made its home in the Speeds.

For starters, this turbocharger is pretty big. The wheels themselves are not large, with the compressor wheel very close in size to the old K04 & the turbine wheel only slightly larger than the K04. However, with the dual inlet turbine housing, 90° compressor outlet, and lots of attached electronics, the whole package takes up a lot of room in your engine bay.

The turbine housing is not far from the old K04. A large five-bolt inlet flange has two rectangular inlets to work with the dynamic pressure system (more on that later) and even a port where the EGR system sources its exhaust gases. The outlet is much simpler, using a five-bolt flange to mount to the downpipe, yet does house a surprisingly large wastegate port.

From a performance standpoint, the large wastegate should help eliminate boost creep but the turbine housing will likely need a larger scroll to get some more serious power out of the engine.

The compressor side is packed full of features. As usual, the wastegate actuator bolts to the compressor housing, however, Mazda has switched to an electric actuator. Interestingly, the bypass valve is also electric and is even mounted to the face of the compressor housing.

Some fancy casting design leaves a pathway between the high and low-pressure sides of the compressor and lets the BPV decide when the passage is open or closed. These two electric actuators will mean easy and consistent boost control. The final plastic component on the housing we believe is a boost assisted vacuum source for the vehicle. Finally, the inlet is a typical clamp connection while the outlet uses a 90° turn and two-bolt flange for better accessibility around the wastegate actuator.

With the housings removed, the CHRA of the dynamic pressure turbo is very simple & standard. Oil feed in the top, two-bolt oil drain in the bottom, and standard crossflow engine coolant ports. The compressor wheel is a cast 6×6 unit and turbine wheel is a basic 11 blade unit.

We are looking forward to waking up the Sky-T in the coming months and making the 2018+ MZ6 into something a little closer to a Speed. Stayed tuned, there’s much more fun to be had from the 2.5T!

-Daniel

Mazda Hybrid?

Mazda 3 Hybrid??

I was looking at the Mazda Japan website the other day and noticed that there is now an option for a Mazda 3 gasoline hybrid listed.  Years ago Mazda announced that they were working with Toyota hybrid tech and this looks to be the result.

There isn’t a lot of detail listed with the description of the model so I decided to do a comparison of the Mazda 3 against the current model year of Prius as the 2 vehicles are most likely running the same hybrid drive setup.

Price:  With the current exchange rate the Mazda 3 hybrid is ~23500 which is almost the same as the current Prius price shown of ~23475.  You get more car with the Mazda 3 for the price and a car which handles like a car should. Win here for the Mazda.

Styling:  Right away I can tell you I prefer the styling of the Mazda 3 over the Batmobile inspired Prius which looks like someone used a late 50s Chevy and applied the styling.  

Fuel Economy: This one is the funniest thing and really shows where Mazda’s engine tech is beating all of the other manufacturers.  Toyota Prius 1.8 hybrid gets 56mpg in combined city/highway. Mazda 3 2.0 hybrid gets 63mpg. Caveat on this data, I took the economy listed on the Japanese page and converted it to MPG so they are not based on the same drive cycles.

If your Japanese skills are on point check out the landing page for the 2018 Mazda 3 Hybrid yourself here.  Just a note google translate won’t let you convert the page due to SSL from Mazda’s page.

So you are asking why do I care about a hybrid and in all honesty I probably won’t own one myself but if it does happen I prefer to at least own one that handles worth a crap and has decent driving dynamics.  I can’t say I have ever heard anyone raving about how good the chassis is in a Prius.

 

-Derrick

*Pricing reflects the current price at the time of writing

New “Mazdaspeed” Finally Coming Down the Pipeline

In case you haven’t heard, Mazda officially announced on November 15th that they are bringing the turbocharged 2.5L CX-9 engine to the Mazda 6.

Now, this announcement did not come with a huge amount of information, but it got everyone here at CorkSport all sorts of stirred up. This fantastic news comes coupled with a new facelift, better quality interior, and a few extra options. Check out the teaser shot down below, in my opinion the CX-5 grill looks great on the 6.

While we do not know if this new turbocharged Mazda 6 will carry the Mazdaspeed badge, we do know it will sure feel like a Mazdaspeed.

The SkyActiv-G 2.5T produces 250hp and 310lb-ft while on premium fuel. That power and torque are more than enough to move around the big CX-9 so it will definitely be interesting in the Mazda 6 that weighs almost 1000lbs less. Two more factors remain for the new 6 to truly be a Mazdaspeed6: manual transmission and AWD.

Since the CX-9 and Mazda6 are based on the same platform and have similar chassis, carrying over the AWD system with the engine is a distinct possibility. Plus, Mazda already offers the 6 in AWD in the European and Japanese Markets. The big question remaining then is the manual transmission. While the manual mode on the CX-9 automatic is nice, it is just not the same as a full-bore manual gearbox. It’s not looking too good as the CX-9 only comes in auto and the teaser images just show an automatic but hopefully Mazda can surprise us with a manual transmission.

Since this 2.5T has been in the CX-9 for a few years now we at CorkSport have had a few opportunities to check out the engine, see how it’s packaged, and look for potential performance gains.

What follows are simply observations that we have made, don’t get too excited (yet):

  • The turbo inlet pipe gets quite small on its route from the airbox to the turbo. Enlarging this would definitely help the turbo breathe better.
  • The exhaust is fairly restrictive at about 2 3/8”.
  • There is a good amount of space where the turbo lives for a high-flow downpipe and even turbo upgrades.

Additionally, this engine was designed to fit in the same compartment as the naturally aspirated 2.5L so we may even get some Mazda 3 love down the road if the SkyActiv-X doesn’t steal every engine bay.

This new Mazda 6 may be coming sooner than you expect.

All Mazda models have gotten a 2018 model year, except the Mazda 6 which is currently at 2017.5 and the Miata that’s stuck all the way back in 2017. Hopefully this means the 2018 model year Mazda 6 has the turbo option. Maybe Mazda is even planning a 2018 Miata update but only time will tell.

Look for more info on the new “Mazdaspeed” 6 during its full unveiling at the L.A. Auto Show on November 29th. We’re just as excited as all of you and to be honest, if a manual option gets announced, one will likely find its way into the garage. Stay tuned to the CorkSport Blog, Instagram, and Facebook to make sure you don’t miss anything!

FACEOFF: 2018 Mazda 3 Touring vs 2017 Honda Civic Hatchback Sport

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 Mazda3 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 = HondaGreen = 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.

Pricing: Honda = $21300  |  Mazda = $21890

SPECIFICATIONS
 2017 Honda Civic
Hatchback Sport
2018 Mazda 3
Hatchback Touring
Vehicle Type:front-engine, front-wheel-drive, 5-passenger, 4-door hatchbackfront-engine, front-wheel-drive, 5-passenger, 4-door hatchback
POWERTRAIN:
Engine Type:turbocharged & intercooled DOHC 16-valve inline-4, aluminum block & head, direct fuel injectionnaturally aspirated DOHC 16-valve inline-4, aluminum block & head, direct fuel injection
Displacement:91 cu-in, 1497 cc151 cu-in, 2488 cc
Manufacturer Claimed Power:180 hp @ 5500 rpm184 hp @ 5400 rpm
Manufacturer Claimed Torque:177 lb-ft @ 1900 rpm185 lb-ft @ 3250 rpm
Chassis-Dyno Recorded Power:180 hp @ 5750 rpm160 hp @ 5900 rpm
Chassis-Dyno Recorded Torque:180 lb-ft @ 3100 rpm175 lb-ft @ 4100 rpm
CHASSIS:
Transmission Type:manual, 6-speedautomatic, 6-speed w/manual shift & sport mode
First Gear:3.6433.552
Fourth Gear:1.0241.000
Final Drive Ratio:4.1053.389
CHASSIS:
Wheelbase:106.3 in106.3 in
Curb Weight:2871 lbs3100 lbs
Front Suspension:MacPherson strut
w/stabilizer bar
MacPherson strut
w/stabilizer bar
Rear Suspension:multilink
w/stabilizer bar
multilink
w/stabilizer bar
Steering Ratio:10.93:114:1
Brakes F/R:11.1 in / 10.2 in11.61 in / 10.43 in
EPA-ESTIMATED FUEL ECONOMY:
Fuel Type:Regular UnleadedRegular Unleaded
City:3025
Highway:3934

To make a long story short, you can accomplish many of the same goals with both candidates, but in two very different ways.

So, whether it’s the brand, the trim, or the balance of style and performance, ask yourself: which one speaks to you?

Let us know in the comments!

-Barett, CorkSport Engineering

* Pricing reflects the current pricing at the time of blog writing