Be careful in giving 100% trust in these AFR gauges. I had mine set where I had 13.0 AFR at WOT because that's supposedly in the range you want to be in from what I read. You would have thought that was enough to give the plugs SOME sort of color. I was WRONG! I pulled the plugs and they were BONE WHITE. They looked like the car was running incomprehensibly lean. I ended up jumping 3 jets in the front and 2 in the rear to get it down to 12.0 AFR at WOT just to get into a safe zone to prevent detonation problems I was having. Don't get me wrong, they are a great tool to have for tuning purposes. I just wouldn't trust all the numbers you read that the AFR needs to be.