If i put in 300 Crude Oil in the Refinery (3x100), furnacesplitter then calculates that 750 wood is need to refine, but when all 300 CO is refined there's always 90ish wood left.

Seems like maybe FB updated the consumption rate and furnace splitter wasn't updated for the change.

I do use QuickSmelt yes, and I did test both plugins seperate.
The furnaces (furni?) is fine and burns perfectly to the last wood, it's only the Refinery.
I played around with the fuel speed and fuel usage speed but it seems like those only work in increments of quarters.
I'll try and play around with the frequencies when I get time.
After all, It is really a first-world problem ;o)