The wood saw on 85mm Wenger Swiss Army knives is about 66mm (2 3/4") long. It is extremely sharp, and cuts on both the pull stroke and the push stroke. Unlike the Victorinox wood saw, it has teeth almost to the very tip. This makes it better for cutting in tight places, though it also means it is more likely to snag on the liners when you close it.
You can use the wood saw to cut wider pieces of firewood by making two cuts in a "v" shape, working all around the outside until it is narrow enough to snap.
WARNING: Use light pressure when sawing, and be careful that the saw doesn't bind, since it can bend at the base and eventually snap off, if pushed with too much force.