91 The graph of the function $y=80 \sin x$ and the graph of $y=x$ have $\qquad$ intersection points.
91 51. The graph of the function $y=80 \sin x$ and the graph of $y=x$ both pass through the origin, are located in the first and third quadrants, and are symmetric about the origin. Since the function $y=80 \sin x$ has a period of $2 \pi$, it is easy to see from the graph that when $x \geqslant 0$, the two graphs have two intersection points in each interval $[0, \pi),(2 \pi, 3 \pi), \cdots,(2 k \pi,(2 k+1) \pi)$, where $k$ is the largest integer satisfying $2 k \pi+\frac{\pi}{2}<80$, i.e.,
$$
k=\left[\frac{80-\frac{\pi}{2}}{2 \pi}\right]=12 .
$$

Therefore, there are $2 \times(12+1)=26$ intersection points.
When $x \leqslant 0$, there are also 26 intersection points.
$$
26+26-1=51 .
$$