Mechanical and KR limits for spark advance

[Gelf VXR]

Would it be safe to say that the mechanical MBT limit can be determined by observing where both the HI & LO maps kave the same cell value, where the cell values differ, the mechanical limit can not be achieved because KR will be encountered berore the mechanical MBT can be achieved. Suffice to say that any increase to the HI octane values in higher g cyl & rpm cells, would yield an increase in torque, but only up until the KR limit was reached, the PCM would adapt to the learned safe maximum spark, not MBT. It is in the low value cells, less than .24 g cyl, where increasing spark advance could overshoot the mecahanical MBT.

[gmh308]

IMHO it would depend which year tune you were looking. GM (& Holden) seem to be running the current engines a lot closer to and even on the knock threshold and letting adaptive controls "fine tune" the timing. Whether they are doing this because of tougher emission standards like Euro IV and/or LEV Bin 2, reach for better economy, or more power, or all 3 is unclear. MBT is probably one consideration but not the only one. In our experience MBT drops off before consistent knock raises its ugly head.

[Gelf VXR]

IMHO it would depend which year tune you were looking. GM (& Holden) seem to be running the current engines a lot closer to and even on the knock threshold and letting adaptive controls "fine tune" the timing. Whether they are doing this because of tougher emission standards like Euro IV and/or LEV Bin 2, reach for better economy, or more power, or all 3 is unclear. MBT is probably one consideration but not the only one. In our experience MBT drops off before consistent knock raises its ugly head. Thanks for your response