The 12Si series is largely consider to be an incremental improvement to Delco's previous 10Si series alternator. The bridge rectifier and cooling holes were enlarged, the fan was modified for better airflow, and there were improvements made to cooling overall. It also featured a thicker stator lamination stack for improved output at low RPM. Despite all these improvements, the maximum safe upgrade amperage for this unit is around 170 amps, but this is will shorten the life of the alternator considerably. If you want more than 140 amps in a durable unit, upgrade to our CS144 series alternator.