i've a wideband lambda sensor, but now is the question what is the best value for power or for fuel efficiently can someone help me?

 

We need more info to help you.

What are your mods?
What is the temps around you?
Standalone or stock ECU?
street car, drag car, race car?

 

For the most part tests in 3 if you can't tune for every gear.
91pump 11.1
93pump 11.1-11.5
100 or above race fuel 12.0-12.5

This is what I tune for, you can run more boost on race as you know but this all depends on your mods also. Hope it helps get you started.

 

i've a full 3" exhaust with high flow cat
run 98 ron fuel
temp around me is 10- 30 degree celsius
1.4 bar boost
stock ecu
safc for adjust a/f ratio
street car and race for fun