Street Tuning, Data Logging, and AFR's
 

When tuning via logs, should I use the the logged AFR's for a partucular rpm as the guide to make adjustments to my map? The reason I ask is because I think that the AFR readings registered for any rpm may be AFR for an earlier rpm level since it takes time for exhaust gas to reach the sensor. Also I think sensor location(houw far from the engine) would also determine this.

What are your thoughts on this, and how do you guys interpret the AFR logs. I use the LC1 System sampling at 1/12 per second. Should I assume logged AFRs for 5000rpm at WOT is actually the reading for say 4800rpm?

You are correct in that there is some lag inherent in the O2 sensor. Unfortunately, this is not easy to quantify. Try holding steady rpm & load points, and averaging 20-50 or more measurements for each "speed / load" cell in the map. This will provide much safer, consistent results, and prevent you from chasing your tail.

The best way to do this is on a load-controlled dyno. Alternatively, you can use hills or brakes to help do this on the road for light loads (BE CAREFUL NOT TO OVERHEAT THE BRAKES by staying on them too long / hard).