So it's a stock z28 and I am wondering if the stock injectors are one hole or 2 holes and am wondering if putting 4 hole injectors in there would help with mpgs and performance

 

I’m not sure which style they they have but I wouldn’t change them out unless they need changing. There won’t be much if any benefit seen if yours are in good working order.

 

They need changing so it's one of those might as well mods

 

If you change to any non stock injector it will require a retune, even if the static flow rates are supposed to be the same for the new injectors. The non linear dead time before opening varies drastically between different injectors that are not the same part number. This can really mess up your idle and transient fueling.