I'm not sure why "lean burn" doesn't do much for normal people, but I can tell you that the p07 ecu for the vx has a whole other chip just for it that no one has been able to figure out how to decode,
Anyway, we tried leaning out dan's stock ecu but it just said no. I just think most engines don't have the combustion efficiency at that range of AFRs, but I'm prolly full of it.