ACT ignition timing corrections

[macromraco]

Hi,

I've seen that my car is always reducing ignition timing due to high ACT. In the ACT Adder table I see that it starts reducing timing at 30ºC, what is in fact a very common outside temperature here:



The IAT sensor is after the intercooler - in the intake manifold - and ACT1 is usually some 15 to 20ºC above outside temperature under boost. It makes me wonder if this table was set up for a Subaru with the IAT sensor in the stock location (reading outside temperatures and guessing the intake manifold temperatures) instead of one reading the current manifold temperature, and is consequently reducing the ignition timing too soon.

Does the table above looks correct for the sensor in the manifold? If it doesn't, could I move the corrections a bit further to reflect the readings done after the intercooler instead of outside temperature?

Thanks in advance.

[pat]

Marco,

If you live in a warmer climate then you may well want to adjust the Air Charge Temperature Adder to suit your local climate. It is pointless in having it always pull timing in what you consider "normal" weather conditions.

Please note that the ECU has *both* IAT and ACT sensors available, you seem to be using these terms interchangeably when they're not the same. ACT is used for density correction, whereas IAT could / should be used for boost control. With regard to ACT, neither the Subaru IAT Sensor locations in the MAF or air inlet, nor the Subaru ACT sensor (as per later JDM STi models which had it) location in-manifold is suitable. The only proper way to measure ACT is after the intercooler, in a location not prone to heat soak - because the MAF based one is pre-intercooler and the late model ACT sensor heat soaks, neither of them are suitable for proper density correction.

The table is populated for a typical engine and the way it reacts to higher charge temps, but as mentioned above, you can change it to suit your local environment. If you want it to work properly then you'll need to move the sensor into a more suitable location.

Hope this helps.

Pat.

[macromraco]

Hi Pat,

Thanks a lot for clarifying the differences between the two sensors, and for all the explanation about them.

I have an early Impreza model and the IAT sensor was removed. The wiring was reused for an ACT sensor installed between the intercooler and throttle body, but it is still subjected to some heatsoak. I'll relocate it to a better place as well as make the adjustments to the ACT timing corrections to better suit the local environment.

Thanks again.