What method were they showing? Boring head, Cam-Calc (where the head is raised and lowered) CNC or something else?

Model engine news an article by graham meek for one but there are more out there. HMEM. Motor boys etc.

Search “Hoglet cams” on Youtube there are several there using that method. Same way I did mine.

Cam forms are quite complex, on high speed engines; to prevent valve surge, and to keep the forces between follower and cam to acceptable limits.

Ideally the valve opens to full lift, almost instantly, and closes in like manner, but the forces involved in even approaching this can be huge.

The faster that you try to open (or close) the valve, the greater the forces to accelerate / decelerate it, and then lubrication breaks down, and wear sets in, if the rest of the valve train doesn’t suffer damage from the forces involved (bent /broken push rods, rocker pedestals, and rocker levers, for instance).

Overhead cams, acting directly on a bucket type valve cap have much lower inertia than push rods and rocker levers, hence their use for high speed, high specific output engines.

But for most of the small four stroke engines that are modelled, high speeds will not be required, fortunately, nor high specific outputs. But “round the pole” racing cars, or hydroplanes can bring problems more akin to full scale.

Howard