Spent a few hours today getting really bad fuel economy in the name of getting good fuel economy.
Fuel maps exist because O2 sensors are only reactive. The ECU needs something to start with as the engine moves through various load and RPM. Sensors adjust the maps for environmental conditions, but having a map that's off has some implications. For instance, having the engine run rich every time the throttle is moved until the O2 sensor has a chance to correct it is a good way to get terrible fuel economy by dumping bunch of unburnt fuel into the exhaust.
I've read that many consider a 10% fuel trim (adjustment) to be acceptable in terms of throttle response and economy, and only bother getting it really close under wide open throttle for safety purposes - running lean at 7,000+ RPM with peak cylinder pressure is a quick way to blow up your engine. My goal is 2% or less, with the majority of cells reading 0 +/- 1%.
I found the biggest hill nearby and for around 4 hours, drove up one side, down the other, then back, then adjusted the fuel maps, rinse and repeat. I've mapped 5 different intake cam angles (0-40) from full vacuum to WOT, from 0-7,000rpm. Ideally I'd do the same thing above VTEC changeover for those cam profiles too, but frankly I just need the line of the curve for wide open throttle and the cell or two next to it, as otherwise I have no business being in the 5,000-7,600RPM range.
I also pulled an ignition timing map from a thread on Hondata's forums, from someone with a somewhat similar engine. My desired air fuel ratios are much leaner at WOT (only 13.5:1!), and the first time up the hill, after VTEC engagement it sounded like someone very angrily shaking a coffee can full of marbles, so I put ignition back to much more conservative timing.
I expect the curves of these fuel contours may clean up a little over time, but this is basically how my engine breaths at various cam angles:
(40 degrees is the one with the horn at the top left, 0 degrees is the more smooth curve)
The fuel maps basically also represent the torque curve, for what it's worth. Having a movable cam allows for the point(s) of peak torque to move around, both with load and RPM.