At the AFR point where the engine makes maximum power, the timing will be at its slowest point . For MIXTURES LEANER OR RICHER than the maximum power point the timing has to be advanced.
Where to tune.
Any ECU looks at RPM and load as the basic input signals. “Load” is the word used to tell how hard the engine is working. “Full-load” means that the throttle is fully open and the engine is making as much power as possible at that specific RPM point. “No-load” means that the throttle is closed. Any point between these two points is referred to as “part-load” or “light load”. Below is shown a timing map.
As an example in the map above at load-site 2,
speed-site 6 the ECU will make the timing 24 degrees “BTDC” . NOTE: The maps in the Unichip look the same except they are modification maps. In other words
the maps inside the Unichip modify the maps in the original ECU. If all the Unichip maps are filled with zeros the original ECU still works like normal and the engine will be standard. If you have a value of +5 in the Unichip’s timing map it will make the timing faster by 5 degrees than the original map. So if the original map has a value of 20 for the timing and the Unichip map has a value of + 5 the timing on the engine at that point will be 25 degrees BTDC.
SAFE AND DANGEROUS
On a petrol engine richer mixtures are safe, leaner mixtures are dangerous. Fast timing is dangerous and slower timing safe.
Light load is safer than full load. At full load the engine works harder and the combustion chamber pressures and temperatures are higher.
The higher the RPM the more dangerous it becomes. As the RPM goes higher there is less time for the combustion chamber to cool down between power strokes.
Before we can start tuning we need to understand the role of temperature
on the AFR. Warm air is less dense and therefore has a lower mass per volume
than cold air.
If you start tuning a engine at say 50 degrees Celsius at 2000rpm the engine will
draw in ”x” cubic meter of air every minute.
After running for 10 minutes that same engine now has a water temperature of
90 degrees Celsius and still draws in the same “x” cubic meter per minute at
2000rpm , however the mass of the air will be much lower and hence the AFR HAS CHANGED. Therefor start tuning with the engine at normal working temperature and maintain it by using a good cooling fan on the Dynometer.
Our problem with temperatures when tuning is how the original ECU changes the
timing or fuel when the engine gets hotter than normal.
Most ECUs will make the engine richer, the timing slower or both when the water
temperature goes above a certain point. Whenever we map an engine it is very important that we keep the water temperature in the normal range.