I have put my engine back together - finally. It has a compression ratio of 10.2:1, runs 98 octane, one step cooler thermostat (86C?) and a 208/198/114 cam. A cold compression test gives an average of 220 psi.

I am self-tuning my TI Performance J3 chip and would like to find out what total timing works best. At WOT, I have set the timing in the chip at about 22 degrees at peak torque rpm, increasing to 25 degrees at peak horsepower rpm. From memory, this is not much different from factory specs.

I have received suggestions of about 34 degrees timing. That sounds like what the iron head pushrod V8 guys run. But sounds a bit much for the 4.0 SOHC six. Especially at 10.2:1, I would expect problems with detonation.

I am assuming that the commanded timing in the ECU/chip includes the base timing (10 degrees). But maybe that is not correct, and the two added together. That is, I might already be at 10 degrees base PLUS 25 degrees ECU = 35 degrees total. Which is correct?

Based on your experiences with the six, what should I be aiming for?

Thanks for the help.

Thanks to Jason at TI Performance for answering this question by PM.

The commanded timing in the MBT Spark Table is the TOTAL timing, including the 10* base timing. The reason total timing for the 4.0L is less than for an iron-head V8 is the much more efficient engine design (especially the head). This is the same reason that a Chevy LS engine needs less advance than a Chevy small block.