I used an S-AFC II for a while, but I used ballpark figures from an equation for my fuel. It was definitely on the rich side of things. Anyway, I think in order to use the unit properly, you have to have an ignition retard module as well. I used an MSD BTM with the SAFC and had it running well enough to get my Z down to a low 14 second 1/4 mile, but I'm sure I could have cracked 13's had I used a wideband to fine tune the fuel up top. Btw, this was on an '84 Z31T ecu on a 280zx. I now use an ecu tuned by Bernardd. The 240sx forums are where I got most of my info on the SAFC.