Effect of larger exhaust on afr

[Bigsi15]

Hi guys
So my exhaust isn't long for this world and it seems the right time to go full stainless turbo back. Was thinking 2.5" due to costs but I was wondering will this larger freer exhaust have much effect on air fuel ratios in regard to running richer or leaner? I can't monitor mine so wouldn't want to run lean without realising. Iv done some googling and it's not given much definitively

Car is a 96 850 t5

Thanks guys!