[axsaxoman]

you can get gains but not by using std ecu +narrow band --you are stuck with the preset lambda values .
std ecu runs WOT too rich to be honest -
it is quite normal for customers to remark on the better economy after having fitted t/bodies --when cruising back home --thats because we have better control of fuelling than the std ecu .
you can run 16-1 or 17-1 on LIGHT cruise ,but NOX levels rise --thats why 14.7 is lambda 1 and what std cars are set to--for emission regs