Jay Chen peppers his conversation with references to the turbocharging death spiral, charge scavenging, the flapper door, and high and mild intentions of A-pedal impressions – A pedal as in accelerator pedal.

His colleague, Dave Coleman, also digs into the horse-and-rider metaphor. It serves to describe what he, a veteran Mazda Motor vehicle dynamics engineer, and Chen, a powertrain guru, are aiming when they tune Mazdas in general, and the 2021 Mazda3 Turbo in particular.

The view to the cockpit.

The horse-and-rider bit in fact speaks to the relationship between car and driver. Jinba ittai does not simply translate to horse and rider, though.

Given the complexity and richness of the Japanese language, the term suggests a bond or deep connection between animal and human, a symbiosis, a sense of perfect harmony. “Zoom-Zoom” is the shorthand for all this, though Mazda now downplays this pop-culture relic from the 1980s and ‘90s.

Chen is head of powertrain performance at Mazda’s North American operation, Coleman his counterpart in vehicle dynamics. They are gearheads of the finest kind, passionate and, I think, grateful to work for a car company that, in this emerging age of artificial intelligence and self-driving, unapologetically tunes Mazdas to support the driver, not replace her. Or him.

The Mazda3 Turbo (starting at $32,900) is, arguably, Mazda’s most significant assault on the Germans in general and the low end of the premium market in particular. Mazda hopes you’ll cross-shop the 3 Turbo against Audi’s A3, Mercedes-Benz’s A-class, Volkswagen’s GTI and perhaps Acura’s ILX, among many.

At 250 horsepower and a very healthy 320 lb-ft or torque (using premium fuel), Mazda’s new turbocharged compact sedan and hatchback (called the Sport) is notably more powerful than the base turbocharged A3 sedan (184 hp/222 lb-ft) and less expensive (the A3 starts at $34,500). True, the Audi brand has more cachet, but strip the badges off these two and you might say the Mazda is the fancier car. Prettier, certainly.

Mazda3 Turbo.

What Mazda hopes you’ll embrace: the Mazda3 Turbo is close to or even better than the A3s of the world in terms of performance, styling and refinement. And it’s certainly a cut above the swath of Civics, Toyota Corollas, Hyundai Elantras and so on – cars which sell globally in the millions.

This new ride, says Chen, “Opens the doors to more premium buyers who appreciate handling, styling, value, but expect the same performance as the commodity cars in this segment.” You heard that. The Civic and Corolla are commodity cars.

The 3’s turbo is essentially the same design you get in the CX-9 SUV (sport-utility vehicle), which also shares a very versatile platform. Yes, turbocharging a 2.5-litre four-cylinder creates more power by force-feeding air into the combustion chamber. But no, the goal was not to create more wide-open acceleration.

What Chen and company have done, he notes, is create a car that “has the potential to go very fast with very little effort. More importantly, it lets you control the speed, the acceleration, and how that acceleration is delivered – what we call jerk – in a precise manner.”

A great deal of clever engineering went into making a turbocharged compact with compression numbers that best a Porsche 911 Turbo. I’ll get into the details later on if you want to geek-out. But for now, this is what Chen says about the 2.5-litre four rated at 250 horsepower/320 lb-ft of torque with premium fuel, 227/310 with regular:

“This is an engine that’s focused on a wide range of driving conditions. For everyday driving, and not meant for high speed hot laps all day long,” says Chen, adding that the six-speed automatic transmission has been beefed up to handle the extra power and torque, before delving into the software story which is at the heart of powertrain tuning.

Handsome.

As for Coleman, the lead dynamics engineer, he echoes much of Chen in underscoring the importance of Mazda’s commitment to a deep study of “the human side of that human-car interaction so we can understand what the car needs to do with the human at a fundamental level.”

Whew!

This brings us to Minimum Jerk Theory, which looks at the patterns of human motion – the kind of stuff robotics engineer study as they work at making robots move like humans. Simplified, Jerk Theory helps car engineers figure out how passengers and drivers physically respond to movements of a car.

Knowledge of how the human body responds sets the target for how the steering, braking and suspension should behave.

“So instead of instrumenting the car, we actually instrument the passenger’s neck muscle” in testing, says Coleman. Mazda’s dynamics engineers aim to create a car that responds in ways that are predictable, that are matched to that subconscious balance algorithm in the brains of driver and passenger.

“If we tune the car so it’s talking to your subconscious properly, you’ll see that you’re able to anticipate that motion and you’re able to ramp up the activity in that neck muscle properly,” he says.

In search of balance, Coleman says his team dialed backed the initial steering response, and then sped it up after the initial turn in.

“So, we’re building this curve that starts gradually and then starts to ramp up just like human motion.”

The tires, the suspension, and all the other pieces that together dictate vehicle dynamics, should work together. He argues that in the 3 Turbo, the engineer goal was to create ride and handling behaviours that are consistent, that don’t “throw any stuff into our subconscious, so that we’re not surprising the balance centre of our brain.”

Yes, Coleman’s team played with the tires, bushings and suspension geometry to handle the Turbo’s greater output. They also worked on the all-wheel-drive algorithm to maximize the downforce on tires at the right moments, to take best advantage of grip as forces change when accelerating, stopping and turning.

And then there’s Mazda’s G-Vectoring Control or GVC, which automatically shifts load onto the front tires every time you turn the wheel. It’s a tiny shift, but pulling just a little engine torque out of the deal makes “the tire behave consistently, makes the steering feel better, communicate better and respond better, more consistently. “

Details? The 3 Turbo is slightly heavier, so Mazda increased the front spring rate by about 15 per cent. There are stiffer dampers to control weight and tighten handling, a more rigid steering arm and retuned steering calibration for more weight and aggressive driving. The GVC is more aggressive, too –slightly heavier steering effort and more aggressive at the initial input.

Human-centered design.

As I head out for a long drive in the new Mazda3 Turbo, I’m given a challenge by Coleman:

“Test this theory. Drive, step back and observe yourself. Notice how many times you’re having to correct and adjust the steering…

“With the Mazda3 you’ll tend to stay very clean. What are your inputs through the corner and do you come out with very few adjustments. That’s because the car is really communicating with your subconscious. It’s doing exactly what you expect it to do. It’s behaving very honestly through that corner. It’s very planted. A simple cornering feel.”

I’ll let you know if the Mazda3 Turbo lives up to expectations.

INSIDE THE TURBO STORY OF THE MAZDA3

If you know your turbos through the years, you are well aware that laggy responses, torque steer – the steering wheel being yanked about in hard acceleration – and frequent gear changes have all been problems in many forced-induction cars. Nothing about laggy turbos screams “premium.”

So, Mazda, says Chen, aimed for a car that has the “direct, abundant torque feeling of driving a larger displacement, naturally aspirated V-6 in a vehicle segment (compact cars) and automotive environment where that basically doesn’t exist anymore.”

Perhaps most important of all, given most drivers spend the majority of time in traffic, the 3 Turbo had to have “almost the same performance below 4,000 rpm” as above, and it had to be happy running on low octane, cheap regular gas (putting out 227 hp/320 lb-ft torque).

In a nutshell, Chen’s team had to figure out “how to put a bigger displacement feel into the downsized turbo engine.” The key piece in all of its: “When it comes to street driving, torque goes a long way and that torque needs to at an engine speed that you’re regularly driving at. Usually below 2,000 rpm.”

So, what did Chen et al do?

First, they increased the compression ratio to a lofty 10.5:1, which is Porsche 911 Turbo territory (10.2:1 on premium gas) and a bit more. Second, they needed to employ “a fast-spooling turbo system that can fill in the gap but is also big enough to continue to build power and torque over a broad range of engine speeds. So, the engine doesn’t feel like a tractor motor.” No turbo lag, in other words.

The high compression ratio in a downsized turbo boosts fuel economy by cramming more air-fuel mixture into the engine, but it also creates cooling issues. Again, if you know turbos through history, a big problem is heat and the damage it can cause – including early combustion, or knock, that can damage an engine. Badly.

And remember: a turbo takes hot exhaust gases to spool up an impeller that pushes more air into the engine. That exhaust air is sizzling. One common solution is to reduce compression in a turbocharged engine – to something like 9:1, notes Chen.

“This kind of approach can lead you down this kind of turbocharging death spiral – of less compression, more boost, more ignition retard, higher EGR and subsequently more fuel cooling which is basically taking away the advantage of a downsized turbo. You’re using more fuel to cool things down to control knock and the point of the downsized turbo was to save gas,” he says.

As I said, Chen lives in a world of crank shafts and connecting rods.

To cool things down to prevent knock without leaping into a death spiral, the team did a bunch of things. One is the cylinder head which has a 4 to 3 to 1 merge of the exhaust ports prior to the turbo. The idea, he says, is to “scavenge as much of the hot exhaust gases as possible, replacing them with cooler fresh air on the intake side.”

Sounds simple, but the execution details are complex – too complex for this space. The story boils down to taking cooler fresh air from an adjacent cylinder at the proper point. It’s an engine design thing.  The team also designed a way to cool hot EGR gases (exhaust gas recirculation) that normally get burned a second time for emissions reasons.

Then they needed to deal with turbo lag – that dead-ish time gap between when the engine responds to your throttle input naturally and when the turbo really spools up to increase torque. No one likes jerky acceleration, but cars with lots of lag are uncomfortable and unnerving.

“We needed to find a way to build a Goldilocks turbo system that is responsive off idle but also delivers the power of a big engine,” says Chen.

This brings us to the flapper door or ejector. In a nutshell, the flapper door stays closed when the exhaust flow is low but open at a higher rate because of the 4:3:1 design and one or two other engine design flourishes. The design here is intended to optimize the exhaust gas flow velocity. As the engine revs up and exhaust gases increase, the flapper door opens and exhaust gases hit the turbo impeller wheel, spinning it up faster and creating more power.

A last thing that’s unique to the Mazda3 Turbo: the intake charge is cooled by an air-to-water intercooler system integrated into the intake manifold. Better cooling means better engine responses – power delivery.

Software and tuning? This is “how we try to predict the intention of the driver through input at the accelerator pedal.” Mazda engineering types spend a lot of time trying to imagine, anticipate and ultimately “Interpret the type of acceleration that the driver is requesting” with their foot. Mild intentions or small impressions at the throttle pedal are for everyday driving in traffic, while large ones are what you do on when going flat-out on a winding road.

The software interprets the drive’s intentions, managing engine responses and shifting.

“It’s how each company approaches the software and the tuning that really defines the brand DNA and how good or bad the car ultimately drives,” he says. “Every company has a focus and a flavour for how they tune the vehicle and that ultimately results in your sense of driving pleasure and your connection to the vehicle.”

You can assume that Mazda believes it has the best formula here.