Charge Temp Approx table tuning using ECT

[Scott33]

My car has a controllable thermostat that can vary from 80C to 110C.  Will I get reasonable results tuning the table by varying ECT instead of IAT?  Or does ECT have other effects on volumetric efficiency that would yield poor results?

I do have a separate oil thermostat and oil cooler so I expect the oil temperature to be fairly constant.

I use case is road racing, so warmup really isn't that important.  OTOH correct performance when ECT is varying (maybe I'm in a draft, maybe it's just hot outside and the radiator can't keep up) is important.  I have gotten by for the last year with just warm up enrichment by ECT at 70C and below, and charge temp and IAT comp tables filled with 0.

 

[Adamw]

It doesnt sound like you understand the purpose of the charge temp approximation.  What we need to know for correct fuel delivery is the temperature of the air that is entering the combustion chamber.  After the air passes the IAT sensor it is further heated by the hot intake manifold and intake port walls which are usually somewhere closer to coolant temp.  The slower the air is moving through the engine, the more heat it picks up on the way in. 

So, the charge temp approximation table represents the contribution that ECT has in determining the charge temperature.  A value of 100% in the table means the charge temp will be the same as ECT, a value of 0% means the charge temp has picked up no heat from the coolant so will be the same as IAT.  

At low load/RPM, the charge temp approximation value will be somewhere close to 100%, and this will fade away to fairly small numbers at high load/RPM as the air is moving so fast there is not much time for it to pick up heat.   

[Scott33]

I think I know the purpose of the charge temp approx table; I have read the help and other threads on the subject multiple times.  I'm not sure what in my question gave you the impression otherwise.  The point of the table is that both IAT and ECT contribute to the actual air temperature and thus density of air entering the combustion chamber.  My question was just whether one can hold IAT constant and vary ECT (and monitor lambda) in order to tune the charge approx table instead of holding ECT constant and varying IAT.  On the surface it seems that either method should be valid.  As you point out, at idle (low load/RPM) the ECT contribution is higher, thus varying the ECT should show a large change in lambda if the charge temp approx table is set to 0.  As the value is increased (and the corresponding values in the fuel table adjusted) then lambda shouldn't change as the ECT varies.

My question is really just if changing the ECT would have other effects on how efficient the engine that wouldn't (or shouldn't) be captured by the charge temp approx table (but instead by ... ? what? a general ECT compensation table?)

[Adamw]

Sorry, the question didnt come across clear to me.  

Yes for the purposes of tuning that table it would be just as correct to vary the ECT while holding IAT constant as it would vise versa, but you will need to hold it at stable temps for quite some time to ensure the port and manifold walls are close to the displayed ECT.  This is why it is generally easier to hold ECT constant and vary IAT as IAT can change very quickly.