| 00:00 |
- If you're really interested in making lots of power, it's hard to ignore forced induction where the engine is fitted with either a turbocharger or supercharger.
|
| 00:10 |
Simply put, forced induction allows more air to be packed into the cylinder in turn allowing more fuel to be added and the result is more energy can be harnessed from the combustion event to give us more power and torque at the crankshaft.
|
| 00:26 |
There's a lot of misunderstanding when it comes to tuning a forced induction engine and the reality is that it's actually no different than tuning a naturally aspirated engine.
|
| 00:37 |
It's just that the air-fuel ratio that we need to target will be different and the amount of ignition timing the engine needs will also be different.
|
| 00:47 |
When it comes to choosing an air-fuel ratio, what we're trying to do is match the amount of fuel we're adding to the amount of air entering the engine.
|
| 00:57 |
As we start making more power though, we also need to consider the combustion temperature.
|
| 01:02 |
And we can add some additional fuel in order to help cool the combustion temperature and ensure our engine remains reliable.
|
| 01:12 |
This is why we can expect a turbocharged engine to run with a richer air-fuel ratio than a naturally aspirated one.
|
| 01:20 |
It needs the additional fuel to control the combustion temperature.
|
| 01:26 |
Choosing the right ignition timing is all about trying to start the combustion event at the right point in the engine cycle, so that we can achieve maximum cylinder pressure at just the right time.
|
| 01:39 |
If we do this, we'll end up with the most pressure acting on the top of the piston at a point in the engine cycle where it can produce the most torque at the crankshaft.
|
| 01:50 |
If we get this right, we'll achieve the most torque and power possible from the amount of fuel and air being combusted.
|
| 01:59 |
When we force more air and fuel into the cylinder with a turbocharger or supercharger, we also find that the combustion actually happens faster since there are now more molecules of air and fuel packed much more tightly together in the cylinder.
|
| 02:16 |
This means that as we increase the boost pressure and force more air into the engine, we need to begin the ignition event later in order to still achieve peak cylinder pressure at the right point in the engine cycle.
|
| 02:31 |
So the two trends we see as we increase the boost pressure, is that we'll need to add proportionally more fuel, or in other words target a richer air-fuel ratio and we'll also need to start the spark event later which is referred to as retarding the ignition timing.
|
| 02:50 |
If we understand how the engine operates, why it needs a certain air-fuel ratio and how to optimise the ignition timing, we can easily achieve the correct results regardless what engine we're tuning.
|
| 03:05 |
As the amount of power an engine produces increases though, it becomes much less tolerant of a lean mixture or detonation and what this means is that an engine can be damaged more quickly if we have the tune wrong.
|
| 03:20 |
For this reason, certainly when you're just starting out, it's always safest to hone your skills on a lower powered naturally aspirated engine.
|
| 03:30 |
This sort of engine will be much more tolerant of running for short periods with a lean air-fuel ratio or perhaps while suffering from knock.
|
| 03:39 |
This gives you a larger safety margin if you do happen to make a mistake while you're tuning.
|
