When you're getting up to cruising speed, obviously low revs and high throttle are good for efficiency. A wider throttle opening reduces pumping losses and increases power production to get you up to speed faster. But how far can you open the throttle without the ECU deciding to enrich the air-fuel mixture?
Here's a flawed BSFC map that at least captures the trends correctly. Note the very small number of data points in the area of interest (especially near 3500rpm, 60N-m), and the lack of lean burn.
The ScanGauge's LBN xgauge monitors the voltage of the wideband O2 sensor. It appears that LBN around 80 indicates stoich, below 60 indicates lean, and above 85 or so indicates rich.
I watched LBN while accelerating in 5th gear from 45-74mph. Up to TPS = 65, I didn't see much change in LBN, but above TPS=70, LBN rose measurably.
I propose that, at least for my car with IAT=120F and in the RPM ranges I tested, TPS around 60-65 is the right amount of throttle. Can anyone confirm this? Are there any other indicators of the ECU throwing FE out the window at high TPS, such as IGN?
I'm assuming you've decoupled IMA and ICE with CARD or MIMA. Otherwise the correct strategy is to stay out of assist however you can.