This is a common question. It really doesn't correspond to the stoicheometric ratio, as much as you'd think. Many people new to digital tuning, aren't real familier with the digital accuracy we now enjoy (are cursed by?). What number should you tune to? Well, it depends on what you do, and how pissed off you are about gas prices, and also how much crap (ethanol) they put into your gasoline. This is assuming 0% ethanol. For every 10% ethanol, subtract 0.5 points. Normally, with a NA engine, you want a slightly lean mixture at part throttle (15.0-15.5 :1) and slightly rich at WOT (12.5:1). This will keep you safe, and give you plenty of power. Normally, you don't want to stray more than about 2 points away from 14.7, and you'll stay safe. Agressive: while still NA, at part throttle, low load, you want (14.7-14.5 :1), then at high load/WOT, 11.5:1. This will use a lot of fuel, but it'll give you lots of torque and power. Low Fuel Usage: If you're like me, and you drive about 100 miles a day, at 100mph average sustained speed, fuel efficency is a priority. This is where you lean out the tables, and advance timing, but we won't get into timing. NA, part throttle/low load, (16.0-16.5 :1) then at WOT, no richer than 12.5:1. Personally, I was running 17:1 part, and 14.0:1 WOT. Not much power, but better FE. Alternatively, you could just lean out the part throttle, and try not to stomp on it. Here's a chart to get a good idea: Here's a chart for those of us who run E10: Enjoy. Happy tuning.