My Megasquirt adventures over the years

I just went searching through the MS source code to try to figure out what is actually going on with that correction factor and it's fairly simple. The curve basically just tells the computer whether to use the MAT/IAT sensor value or the CLT sensor value for the air temp in the fueling calculation. So 0% means full MAT and 100% means full CLT.

My next question is whether you can use negative values or not. I don't think you can, but I need to double check. The main thought process there boils down to where your air temp sensor is. If your temp sensor is outside of the engine bay and reading true ambient conditions, this curve gets pretty easy to use. The lower the air flow, the closer it is to coolant temp by the time it hits the intake valve. Where it gets trickier is if your temp sensor is in the engine bay/intake. I need to see if I can get a thermocouple or something in my intake to confirm this, but the theory is that the sensor body heats up with the engine itself and reads higher than it should due to heat soak, to the point that the airflow around it isn't enough to bring it back down to ambient. So in that case, you'd want to subtract some amount from your MAT reading. In theory you can do that if the curve lets you use negative values, but I have a gut feel that it won't let you.