"aat"

is this measured exterior to the vehicle, or in the intake?

It's in the intake. GM service docs refer to it as IAT2.
The other IAT sensor is the one in the MAF.

Cheers,
Ross

That is what i was wondering. So it IS post CAC. Very odd it would be labled "ambient" though. That makes no sense to me at all.

I agree, most of the LBZ docs refer to them as IAT1 and IAT2, but I did read in one diagnostic chart (can't remember which one), they had it written as "Ambient Air Sensor (IAT2)".

Cheers,
Ross

It is a very interesting adjustment.

I have logged (separate temp logging equipment) post CAC charge at up near 200 degrees. From the table it appears optimum WOT timing goes from 20 BTDC to 40 BTDC with this CAC heat soak.

Does this make sense? I thought increasing charge temp, required timing to be retarded....

By contrast to the LBZ, there are no provisions in the LLY tables to adjust timing for charge temp increase.

You probably had good reason for labeling, but I think IAT1 and 2 would be much less confusing. FWIW.