14.7 is the goal for cars with cat converters. Since we're not running those you can go leaner than that as long as your car will tolerate it without detonating, surging, etc. I tried running mine at 14.7 for a while, then went to 16 and I didn't get any difference in driveability or throttle response. With the thermoquad's easy to adjust primary metering rod tree, the cruise a/f ratio was very easy to tinker with.