Okay. We’re getting desperate now. We don't have a lot of options left.
The only remaining modification is the Traction Control, which costs an absurd 2 million yen…

What is traction control anyway? And why is it so goddamn expensive?

:
This is the traction control system. Electronically controlled to prevent wheel spin. It's a high-tech part that makes it possible.
In modern cars, traction control is a safety system tied with many other electronic stability assistants that can detect whether the tyres have lost their grip from the road and will accordingly cut power or apply brakes to prevent the car from sliding. This invention has saved countless lives and nowadays you can't buy a car without it, but back in the 1990s it was still relatively new technology.
I suspect the modification here is more akin to what we would now call ‘Launch Control' - I.e an electronic system that will optimize the power delivery on take off to minimise wheel spin when accelerating from standstill.
Hopefully this is what we need to fix our performance issues. It seems consistent throughout the game that the other car always beats us on initial acceleration, and our power advantage comes through when the big turbos kick in. Zero 4Champ 2 was all about tuning the car to minimise wheel spin in the different dry / wet / ice conditions, so it fits we have to do it here, and perhaps it's a bit more nuanced since it appears this game is dry course only.
However, since we just spent all that cash on a giant turbo....
... we can't afford it.
Once again, we're going to have to travel to the seedy underbelly of Kowloon Walled City, where the criminal triad gangs roam freely, unburdened by taxes and ignored by the Hong Kong government...
...Oh, and it's also where they breed dragons…

But it's okay, because we now have the ability to summon demons.

And to think, when we started this journey, I thought the fact we were battling mice was ridiculous.
Now with another few floors sanitized through our black magic side hustle, we can turn our attention back to trying to become the fastest drag racer in Japan.

Now, with just under 2 million dollars in credits, we can blow it all on fitting traction control to our car.
…If this doesn't fix our performance issues, we're in trouble.

We now have (basically) every upgrade. That empty slot is for the Auto Clutch, which I experimented with earlier and see as mostly pointless.
Time to test it out on the track…

Yes! Finally! We won!
But let's be honest… only by a bees dick.
Let's try another race…

Another win! But again, only by a razor margin…
And let's be honest, after spending all this cash, these are the same numbers I was pulling in the Celica…
… Is the RX7 no good?
… Or is it something to do with my technique?
I've done some experimenting, using some of the advice here with mixed results - but I think you guys are on to something. The key is finding the right rpm range to shift at for each gear - and the RX7 is different than the Celica in what works. I'll get into this a bit with the next post.