12.8-13.0 n/a and i'd say in the high 11's on spray. Be sure to back the timing down on the n2o and that you have a good fuel pump. I like 255 high pressure pumps.
You can change your a/f on the nitrous by playing with jetting. Also different nitrous pressures will change the a/f. Higher psi will be leaner than lower psi with the same jetting.