Road Tuning: MBT Tuning
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MBT Tuning
02.16
| 00:00 | Before we start tuning the ignition tables, we want to have a quick recap about what we're trying to achieve when adjusting the ignition advance. |
| 00:08 | When the spark plug ignites the air/fuel charge in the cylinder the combustion event causes cylinder pressure to quickly rise. |
| 00:15 | It's this pressure on 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 maximised. |
| 00:40 | The point where we achieve maximum torque is called MBT timing or maximum brake torque timing. |
| 00:47 | It is 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 the peak cylinder pressure occurs at the ideal point and we achieve maximum torque. |
| 01:04 | The correct ignition advance is a constantly moving target as it will vary with rpm as well as engine load. |
| 01:12 | Generally as rpm increases we need to advance the timing as there is less time available for the combustion event to occur. |
| 01:20 | Conversely, as load or air flow increases the combustion event tends to occur faster so we can reduce or retard the ignition advance. |
| 01:30 | To properly tune the ignition map we need to have a sensitive load-bearing dyno that can give us feedback on engine torque. |
| 01:38 | We can't do this effectively on the road, and as I've already mentioned, this is one area that we must make some compromises if we're road tuning. |
| 01:47 | An important point to keep in mind is that too much ignition advance can result in detonation which can quickly damage an engine. |
| 01:56 | Any time you're tuning an engine it's important to use a high quality audio knock detection system to ensure the engine is not detonating. |
| 02:06 | The concept of MBT tuning as well as detonation is explained more thoroughly in our EFI Fundamentals course. |
