You can split the angle
If there are 18 teeth on the cam sprocket then each tooth you advance or retard is a 20 degree change, like TWF says (360 degrees / 18 teeth = 20 degrees per tooth).
If you move the chain on the crank sprocket the change would be 10 degrees per tooth, half of moving the chain on the cam sprocket. This isn't intuitive, but it's true. Moving the chain on the crank sprocket one tooth rotates the crank 1/2 the number of degrees that the cams move when you move a tooth on them.
Whether or not you gain or lose horsepower is debatable until you dyno the results. I would guess this isn't going to be a happy engine.