Practical Standalone Tuning: MBT Tuning Technique
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MBT Tuning Technique
02.10
| 00:00 | Before we start tuning the ignition tables, we want to have a quick recap about what we're trying to achieve when we adjust the ignition advance. |
| 00:07 | When the spark plug ignites the air fuel charge in the cylinder, the combustion event causes cylinder pressure to quickly rise and it's this pressure acting on the top of the piston that provides torque to the crankshaft. |
| 00:19 | What we find is that the engine will make maximum torque when the peak cylinder pressure occurs at a point approximately 16 to 18 degrees after TDC, or as the piston is going back down the bore. |
| 00:31 | At this point, the cylinder pressure can have the most mechanical leverage on the crankshaft, and the result is the engine torque is maximized. |
| 00:40 | The point where we achieve maximum torque is called MBT timing, or maximum brake torque timing. |
| 00:47 | It's also often referred to as minimum timing for best torque. |
| 00:52 | What we're trying to achieve by adjusting the ignition timing is to start the combustion event at the right time so that peak cylinder pressure occurs at the ideal point, and we achieve maximum torque. |
| 01:03 | The correct ignition advance is a constantly moving target as it will vary with RPM as well as engine load. |
| 01:11 | Generally, as RPM increases we need to advance the timing as there is less time available for the combustion event to occur. |
| 01:18 | Conversely, as load or air flow increases, the combustion event tends to occur faster so we can reduce or retard the ignition advance. |
| 01:28 | To properly tune the ignition map, we need a sensitive, load-bearing dyno that can give us feedback on the engine torque. |
| 01:35 | We will see in the next section how we use the dyno to do this. |
| 01:39 | You can't do this effectively on an inertia dyno, or on the road. |
| 01:43 | An important point to keep in mind is that too much ignition advance can result in detonation which can quickly damage an engine. |
| 01:51 | Anytime you're tuning an engine, it's important to use a high-quality, audio knock detection system to ensure the engine is not detonating. |
| 01:59 | The concept of MBT tuning as well as detonation is explained more thoroughly in our EFI Fundamentals course. |
