The problem is that you don't have enough control. You can't just adjust fuel by RPM and expect it to work right. You will only be able to adjust fuel at wide open throttle. This is insufficient. You must be able to adjust fuel by manifold pressure and RPM. With my wideband, you would see your a/f ratios moving around, sometimes too lean, at part throttle- open loop. You can think of the S-AFC as having only one slice of a useful fuel map. You would need several of the same slices, at multiple load values, to complete the map. The S-AFC gets by only because during close loop operation, the factory computer can trim out incorrect offsets that you may have programmed for full throttle. If you are only interested in wot performance, it will work. However, if you want great drivability as well, it is a severe compromise. You will also be relying on the factory computer's knock detection feedback loop to manage your timing. While it's a capable system, I would rather have my own timing maps to make sure things are on the safe side. In fact, you need an equal amount of timing map slices as you do fuel map slices to have a complete system.