Comment by antisthenes

I have a modified ebike with an unlocked controller.

Without commenting on safety, let me just say that 40mph is a fantasy, unless you're going down a VERY steep and long hill. It also requires you to be in a road racing bike position, or air resistance will flat out not let you go that fast (people are quite wide)

But my bike is otherwise stock. There is no extra power added to the stock Yamaha motor (250W rated, ~400W peak power). The only thing that is removed is the 28mph limiter.

The DIY conversions that let you go 40mph (I've seen the videos just as well) are more in the realm of electric mopeds and motorcycles than bikes, IMO.