I feel that this guide is more complex than it needs to be. What did you do to find this technique? I'm curious what the "linear algebra and python simulations" were

There are only 5 bars?

It's been a while since I've played, but I believe you pull it up in the engine shop. Good luck!

how do i pull this up?

You don't have to do that much better to beat the AI every time. But yeah, if you have a general interest in this I definitely recommend this game, since you can tune transmissions and engines for different things and it explains what everything does:
https://store.steampowered.com/app/293760

It's a bit overpriced but goes on sale a good bit

The general principal though is to adjust your gears so that you get as much torque as possible at whatever speeds you'll be driving the car at.

This also means that if you want to be "realistic", a gearshift tuned for drag racing is going to be terrible for anything else. In real life you'd never put that on a pickup truck or a city-driving sedan, etc. In those cases you'd want to have plenty of torque at low numbers, and then probably have the engine at some RPM that's the most fuel efficient.

For actually calculating this stuff, you'll want to be organized with your units or to use a tool like this: https://www.blocklayer.com/rpm-gear

But Tire Diameter matters immensely. And it's a giant pain to convert between inches and RPM and mph etc. So you can always just use trial and error.

That's a much harder topic and unlike carb/ecu there's not a single optimal solution. It depends on what you're optimizing for.

But in general, for drag racing, you want to:
1. Run your engine through the dyno, and ballpark note a few target torque ranges. Maybe it's like:
ideal: 3200-3500
good: 2800-3700
okay: 2600-3900
2. You want to spend as much time in "ideal" as you can. So put your lowest gears in a wider range, since you'll probably not even spend a second in 2nd gear. Whereas you'll be spending a long time in your higher gears
3. For each gear, calculate speed ranges. For example, maybe your 2.41 ratio will be 2600-3900 RPM at 30-60mph respectively
4. Your gears need to meet their "neighbors" at the same speed. if gear 2 is designed for 30mph-60mph, gear 3 needs to be designed for 60mph-whatever.

Can you do a guide on gear tuning?

Same strategy!

what about the carb