i know that the first few minutes of a brand new motor running are crucial for proper ring seating, and that too lean or too rich can be detrimental to the motors health and longevity.

my question is how much room for variance is there in the afr's? is 13:1 too rich? is 15:1 too lean? i will be getting my next motor professionally tuned, but i will be driving it to the dyno and starting it up initially

 

keep it as close to stoich as you can. leaner wont hurt, but too rich will wash the walls.

 

Just stay out of boost until tuning. 14 - 15 afrs when not on boost should be ok. I see lots of dyno sheets showing 11.5 - 12 afrs when on boost in the 6 - 15 psi range.

 

10:1 is too rich

 

14:1 - 15:1 is ideal... just be sure you're around there (within half a point or so)