This article covers why those two things aren't the same, and how learning things in the right order is what closes the gap.

Knowing what a setting does describes the ECU, not your engine

If we take ignition timing as an example, the help file description is correct. The number in the table is how many degrees before TDC the spark plug fires, more advance fires it earlier, and less advance fires it later. What that describes though is what the ECU does with the number, rather than what the number should be for your engine.

The reason the timing table exists at all is that combustion takes time. Once the spark plug fires, the flame has to develop and burn through the mixture, and the cylinder pressure it builds needs to peak at roughly 14 to 18 degrees after TDC for the engine to make its best torque. Timing is how we position that peak, and the minimum advance that gets it there for best torque is what we call MBT timing.

How much advance it takes to put peak pressure in that window then comes down to the engine itself. How quickly the mixture burns depends on things like the combustion chamber shape, where the spark plug sits, the bore size, and the fuel, and at high load a lot of engines reach their knock threshold before they reach best torque, which limits how much advance they'll accept.

None of that is in the timing table, it's in the engine. Every number in a finished timing table is the result of a decision made about one particular engine. Knowing what the table does is enough to let you change the numbers, but it's knowing why they are what they are that tells you what to change them to, and whether they need changing at all.

Knowing what a setting does tells you about the ECU. Knowing why you'd change it requires understanding the engine and EFI system setup.

Following a tutorial works until your engine responds differently

A tutorial is recorded on one engine. The steps it walks through are usually sound, but the numbers you see on screen are the numbers that engine needed, with its combustion chamber, its compression ratio, its fuel, and the conditions on the day it was tuned. None of that is written next to the numbers, so it's easy to treat them as if they apply to any engine.

So you follow the same steps on your own engine and it doesn't respond the same way. Maybe it knocks where the tutorial engine didn't, or it's still picking up torque with more advance at the point the tutorial said to stop. The steps are the same, the engine isn't, and if all you know is what each setting does, there's nothing in the steps that tells you why the result is different or what to do about it, and this is where you start to lose confidence.

Early on I ran into the same problem with lambda targets. Every forum thread, every course, and every tuner I asked had a different number for wide open throttle. Most of them a lot richer than they needed to be, and none of them really explained why they'd chosen it with any scientific reasoning or evidence. Each of those numbers probably made sense on the engine it came from, but without knowing why it had been chosen I had no way of telling whether it made sense on mine. Working out what a lambda target is actually there for, and what changes it from one engine to the next, is what choosing the right lambda for the conditions goes through.

The steps in a tutorial carry over to your engine. The numbers usually don't, and nothing in the steps tells you why.

Understanding why is built in order, not added at the end

What's missing when a tutorial's numbers don't work on your engine is the understanding underneath the settings. Understanding should be built long before you sit down at the laptop. To know why a timing number needs changing you need to understand combustion, and to understand combustion you need to understand how the engine works and the physics behind it. Then, to make a change and know whether it worked, you need to understand how the ECU and the ignition system turn that number into a spark, and how to read the engine's response in your logged data.

That structure is what the EFI Mastery Roadmap is designed to do, with each Stage covering what the next one depends on. Stage 0 starts with how the engine works and the engineering principles that underpin a lot of what is going on in modern EFI and performance engines. In Stages 1 to 4 we move through the fuel and ignition hardware, how the ECU controls the engine, fuel and combustion, and data and analysis, before any calibration work starts in Stage 5. We cover why that order matters, and what goes wrong when it's skipped, in where to start with EFI tuning.

By the time you get to calibrating, you know what physical thing each table is there to compensate for or represent, what factors change that for your engine, and what you'd expect to see in the data if something's not right. That level of understanding allows you to make each decision case by case, on the engine in front of you, rather than copying what worked on someone else's setup. It also means you can watch a tutorial, keep the steps that apply to your engine, and work out the numbers and other applicable changes for yourself, while having the skills to assess changes and understand what's happening with confidence.

You can't add the why at the end. It's built up in order, one Stage at a time, until you can make the call on your own engine with confidence.

Understanding why carries over to the next engine, copied numbers don't

The physics underneath the tables is the same on every engine. Combustion still takes time, peak cylinder pressure still needs to occur in roughly the same window after TDC, and the engine still has a knock threshold, whatever ECU is controlling it and whatever the table happens to be called in the software. If you understand those things, you can sit down with an ECU you've never used on an engine you've never seen, and have a reasonable idea of how it should respond before you change anything.

I've worked on a fair few engines and ECUs over the years, across standalone, OEM, and marine, and the pattern was the same the whole way through. The people who were good at this could work out why an engine wasn't doing what the textbook said it would, because they understood what was going on underneath it. The people who struggled could follow a process as well as anyone, right up until the results didn't match the example. That usually came down to how they'd been taught, rather than talent or effort.

So the next time a tutorial's numbers don't work on your engine, start with what's different about your engine, and what that difference means in relation to the table and what it represents. Once you understand why a setting is there, that question has an answer, and it's the same question on the next engine you work on. "What's different about this engine and how does that change how I approach this tune?"

Key points

  • Knowing what a setting does describes what the ECU does with a particular number. It doesn't tell you what that number should be on your engine.
  • Ignition timing should position peak cylinder pressure after TDC, but how much advance that takes depends on how the engine burns its mixture and where its knock threshold sits.
  • A tutorial's numbers were right for the engine it was recorded on. The steps usually carry over to your engine, but the numbers often don't.
  • Copied numbers only work until your engine behaves differently, and without knowing why they were chosen there's no way to tell which ones suit your engine.
  • Each Stage builds the understanding the next one depends on, so by the time you're calibrating, you can make decisions for your own engine rather than copying someone else's numbers.
  • The physics underneath the tables is the same on every engine and every ECU, which is why understanding carries over from one engine to the next and copied numbers don't.

If there's a specific topic or area you'd like us to cover in a future article or video, we'd love to hear from you. Send your requests through to support@efimastery.com and we'll keep you posted.