13 is lean mate, i would not run an engine in the 13's on boost
, i'd say about 14's on tickover, although my mk1 din't like to tickover that lean, i think it was an airspeed issue due to the large throttle body and big tubby, but once it was moving it was ok, i got it mapped as lean as i could at 70mph untill it started to misfire, then put some more fuel in, it did around 32mpg on a long run.