Changes

Ignition timing is determined by two look-up tables (Ignition timing, low octane and Ignition timing, high octane) and two settings tables (Min octane for adjustable features and Min octane for adjustable features). Within the Simos18 ECU there are additional lookup tables that will impact timing that Maestro does not access. Intake Air Temperature (IAT) as recorded by the MAP sensor is one such variable that will impact your timing advance. High IATs will retard timing to reduce the likelihood of pre-ignition due to high combustion temperatures within the cylinder. The ECU will override the two Maestro timing tables to ensure engine longevity in the face of extreme environmental variables.

The two adjustable tables are preset at 87 octane and 100 octane, but these can be modified by the user. Setting the octane slider at its lowest setting will force the ECU to utilize only the Ignition timing, low octane table when determining timing. Alternatively, moving the slider to its highest setting will force the ECU to utilize only the Ignition timing, high octane table. Setting the slider anywhere in between the lowest and highest settings will allow the ECU to interpolate the timing curve based on air mass and RPM utilizing the two timing tables. Maintaining the stock values of 87 and 100 provides plenty of adjustability for the user and most would recommend leaving these values alone.

The tables have 3 axis:

The two lookup tables serve as reference points for the ECU based on the user selected octane slider. As an example, if air mass at 3000 rpm is 600 mg/stroke and the low table shows 5.250 and the high table shows 13.875 the ECU will then look at the octane slider value and interpolate timing. Keeping the stock settings of 87 low and 100 high there are 100-87=13 different timing values that could be used. The delta between low and high for our example is 13.875-5.25=8.625. 8.625/13=0.66. For every increase in 1 above 87 on the octane slide the ECU will attempt to run approximately 0.66 degrees timing above the value in the low table. If you set the slider to 99 (12/13 available positions) then the timing will be 12*0.66=7.92 added to 5.25=13.17 (Maestro only allows values as multiples of 0.375 so in actuality the timing would be 13.125...close enough).

WARNING...DO NOT ADJUST ANY OF THE TIMING VALUES IN THE COLUMNS BELOW 1000MG/STROKE. Why? Daily driving around town from stoplight to stoplight the engine uses ignition timing fairly aggressively due to the lack of airmass (which is due to the lack of exhaust volume spinning the turbine) to power the vehicle. If you lower these values the car will feel sluggish at part throttle. If you increase these values the engine will knock. Only make changes to the last few columns of the tables.

Use your datalogs to make adjustments as needed. If you are consistently seeing knock in a few cylinders at a specific RPM range then adjust the timing down at that RPM and air mass cell. It's best to make timing adjustments to both tables equally (or as equal as possible). If you are going to pull 1 degree of timing out at 6000 rpm in the 1299 air mass column then pull 0.375 from one and 0.75 from the other. If you feel like you need further reductions then pull more from the table that got the 0.375 reduction. If you only adjust one table then your octane sliders will no longer function smoothly as one end gets aggressive quickly and the other doesn't respond adequately.

This question comes up quite often. The answer is whatever you are most comfortable with. Some people don't want to see any KR. Some people say anything up to -3 degrees in 2 cylinders or less at the same time is ok. Most would agree that -4 or more is not a great idea and one should remedy that. Some cars seem more prone to KR, some at specific RPM ranges that can't be removed with meth or even full E85. You might see one cylinder in particular that has more KR events than the others. Every motor is different. Use your own comfort level when setting timing.