I am a docent at an aviation museum and auto museum. One of my fellow volunteers showed me an unusual aircraft engine. It has no camshaft or rocker arms to open the intake valves. It only has a weak valve spring.
On the intake stroke, the suction of the descending piston is enough to open the valve and let the air-fuel mixture in. On the compression, power and exhaust strokes, the pressure in the cylinder keeps the intake valve closed.
I have never seen this on an auto engine. I can see how it could save a bit of weight which is critical on an aircraft. I suppose it is possible that on the compression stroke, a small amount of mixture could blow back into the intake manifold thereby reducing the volumetric efficiency.
Has anyone ever seen this and why isn’t it used in auto engines?