Resident racer Randy Pobst and I are sitting on two black vinyl bar stools in the cinder block building next to Willow Springs' Streets circuit. He leans in: "It was fascinating to have that engineer sitting next to me, hanging on for dear life, holding a laptop and actually typing into it while I'm driving at speed." Changing its code? "Yes. And I could feel it in the car." He cockeyed-smiles with a sort of amused, "What the heck?" look on his face.

Nearby, the Tesla engineers have more of a look of cool relief. Earlier, a Model 3 Performance—software-flashed with its latest Track mode nervous system and mounted with 10mm-wider Michelin Pilot Sport Cup 2s and track-friendly Brembo brake pads—had lapped the course in a 1:21.49. That hammers the 1:23.90 it set six weeks ago on its standard 235/35-20 Michelin Pilot Sport 4S tires under the software supervision of Track mode's earlier, wobblier prototype code.

See all 31 photos

What no one is quite saying out loud, though, is that a 1:21.49 snips a lifetime-like 1.29 seconds from Randy's recent lap in the Alfa Romeo Giulia Quadrifoglio. The new time essentially matches a 2016 Porsche Cayman GT4 and even beats a former Best Driver's Car winner, the 2011 Ferrari 458 Italia (1:22.30). Until the new BMW M3 shows up, that perches the Model 3 atop the podium as the world's quickest sport sedan—at least around this track.

Exactly 42 days ago, however, the mood here was much darker. By the end of our comparison lapping of the Model 3, Giulia Quadrifoglio, and Jaguar I-Pace, we ended up tiptoeing around a Team Tesla that was in a stoic but quietly pissed-off mood. Not only had the Alfa, with its grip-centric tires, dimmed Track mode's luster, but Randy had also bounded off Turn 11 at 90 mph after a couple of road undulations discombobulated the Tesla on its fast approach into its brake zone.

None of this sat well with the engineers. Nor, one suspects, with Elon Musk. When Randy's hot laps in the original Track mode car were done, he rolled in to the pits. I opened the passenger door to pop the memory cards from the Vboxes and glanced up at him. He was already staring down at me with that pent-up laser look from his black open-faced helmet when he's about to say something he really, really means. "Kim," he started, "these guys should hire me."

Elon must have been thinking the same thing. A few days later I got an email from Tesla asking for Randy's contact information. Then a couple weeks after that, Tesla said they were renting Willow, hiring Randy for a day of development driving, and inviting us to come watch—if we behaved ourselves.

See all 31 photos

See all 31 photos

Twelve of us showed up. "You never told us you were bringing 12 people!" the Tesla PR rep chirped. But it was too late. Our photographers and videographers were already arriving and unloading.

The day's agenda would progress in methodical stages. First, Randy takes familiarity laps in a Model 3 set exactly as it was on September 17. Then he moves to another car to confirm that Track mode's updates are hitting their marks.

Randy then moves to yet another car sporting that updated software, the Pilot Sport Cup 2 tires, and a set of track-ready Brembo brake pads (which results in the 1:21.49).

After that, it would be lapping and experimenting to start shaping a future software update. In total, three Teslas were tag-teaming through the lapping, as software, tires, and pads are swapped, the battery packs supercharged to 95 percent capacity (giving the battery room to absorb regenerative energy) and thermally preconditioned (cooling both motors and the battery; underway, the hotter motors use the big battery as a heatsink).

See all 31 photos

See all 31 photos

The Alfa's 1.12-second advantage back in October wasn't all that terrible, considering that the Model 3 Performance's everyday tire is necessarily a Swiss army knife of vulcanized rubber—simultaneously good for ride quality, quietness, grip, and that ever-critical low rolling resistance. But against the Alfa's mission-specific, asphalt-biting Pirelli P Zero Corsas, it's a really nice Swiss army knife brought to a gunfight.

Watching Tesla struggle to offer a track-oriented tire has been curious to watch. For energy-scarce electric cars, efficiency is their touchstone. Raising your hand in an engineering meeting to suggest a sticky tire that'll shorten an electric vehicle's range by maybe 12 percent will get you quickly walked to the parking lot with a small cardboard box filled with your family photos. But look at the two tires' peak grip around the track's final corner (aptly called the skidpad): 0.90 g versus 0.96 g. That's the brass ring.

I brought along a little model of a Tesla and handed it to an engineer, asking him to act out what exactly is going on as Track mode traverses a typical corner. Immediately, there's something to explain. Track mode noticeably amplifies lift-accelerator regen, which eases the thermal load on the brakes. But it also shrinks the transition from acceleration to braking into a blink: just lift your right foot. Couldn't be quicker.

See all 31 photos

Angling into the corner under braking, Track mode seems to illogically instruct the rear motor to briefly overpower the rear, stepping the tail out a few degrees to target what the math model thinks is the maximum available lateral acceleration given the suspension's compression. Then it tailors that prediction by analyzing the tires' actual slip rates. Post-apex, the front motor takes the lead role, delivering just enough power to cause a muted understeer, pulling the car out of the corner as the rear motor ladles in what's needed to maintain that attitude.

This simple ballet is kept carefully balanced from entry to exit by the lightning responsiveness of the electric motors and brake pads that individually and automatically kiss their discs to laterally redirect power across the open differentials. Only a from-scratch, fully integrated solution can keep all these balls in the air. (It makes me really wonder what Porsche is doing to make the Taycan handle around the Nurburgring). According to Tesla's calculations, Track mode lets the car apex earlier and begin accelerating sooner.

That's the engineer's version with his hand sliding a model car across a piece of paper.

See all 31 photos

Randy, from his perch on that barstool, explains the same thing but in its full-scale, tire-screeching, g-tugging, adrenaline-addled reality: "That prototype version of Track mode a few weeks ago was … inconsistent. I had this distinct impression of approaching a corner flat-out and thinking, 'I wonder what's going to happen?' But this one (with the updated software) is far, far better."

The engineer explains that to provide more driver confidence, the software does not tiptoe quite so close to the edge. As part of his consulting work, Randy notes: "One thing we did was reduce the regenerative braking at lower speed. There's naturally less of it at higher speeds because the battery can't absorb that rate of power. But the last time we were out here, the car kept slowing down a lot when I'd lift off the accelerator; they showed me the data, and it's about 0.3 g of deceleration. The trouble is that I'm a trail-braker, and it's adding that strong brake force while I'm turning. Now it's less, more like a normal car's engine braking. This is a huge step forward.

"At first there was too much front regen, which made it pushy on the entry phase, so they shifted it to the back," he continues. "There's a tremendous amount of torque here [450 hp and 471 lb-ft of torque], so the car can be slid around a little bit—but actually not that much because the front motor comes back in and balances everything out. At the apex, it has a little bit of initial power oversteer from the rear motor, then it fixes itself and wants to power understeer. We made some progress on refining all that. I tried the car on the Pilot Sport Cup 2s and Brembo pads, and it was really hooked up."

As for braking over that double bump at the end of the back straight (the site of his prior off-track excursion), how was that situation accounted for?

See all 31 photos

"When you're straight and balanced, the car stops extremely well with a hard attack of the pedal," Randy says. "But in a corner or over a bump, I want to lay into it softly so as not to instigate the ABS. When the car is lightly loaded [cresting a bump], there's more ABS intervention than with the supercars we sometimes drive here. After talking to the engineers, I started braking after the first bump and straightened out my line in the brake zone so I didn't have much cornering load, which helped a lot." Although the Model 3 doesn't feel as heavy as it actually is, nevertheless, the weight of a battery-electric car invites this sort of ABS moments as it heaves over undulations.

There's nothing at all new about a racing driver developing the chassis of a high-performance car; adjusting anti-roll bars or tuning shocks at a racetrack are part of the checklist. But on October 5, at Streets of Willow, we opened the door to a new place. Computer code and human instincts confronted each other. The millions of lines of Tesla's Track mode software were amended instantaneously by a guy with decades of experience, someone who may have danced more different cars around racetracks than anyone on earth.

Here's the coolest thing: Less than a week after that test session, Randy's tuning expertise will be available to all. Today—November 8—Tesla expects this "Release Version" software to be accessible to owners of all Model 3 Performance cars (with the redundant-sounding Performance option, now standard). The combined wizardry of engineers in Fremont, California, and our own Randy Pobst is being beamed via over-the-air updates. All you have to do is find a track and push a button.