as for the AFR check, you'd need non-std equipment to do that as the nitrous content in the exhaust gas confuses your normal lambda readings... makes it read rich when it aint. i beleive you can buy special (and VERY expensive) equipment which means you can get round this tho...

a few rolling roads have blown up nosed engines that way.... thinking its rich when its not so leaning it off till it goes pop

just a little unrelated bit of info for you there... lol