Setting the A/F ratio?

[alundra]

I'd like to set my air fuel ratio.

My mods:

MK 1,5
Stock ECU management, stock injectors, K&N filter in box, 2.5" piping+ intercooler, polished head, cold spark plugs, T2 at 0.6 bar with MBC, 2,5" exhaust, 98 RON, Luk 13 clutch, 40 mm dropped etc...

I have a digital A/R ratio gauge, idle 14.6, full throttle/full boost 10(can't read under...). i'd like to set up like 12.5/13 at full boost.

What can I use? (cheaper to higher cost)

Cheers.