12 Valve version
There were also a lot of them from different manufacturers. But one of the most massive was the powertrain of Hyundai Accent. However, the company did not develop it further. The name of the engine from Hyundai is G4EB (there were other modifications, but the timing system is the same). There are two valves at the inlet and one at the outlet. And here one shaft is used and there are hydraulic compensators. The volume is 1.5 liters (90 hp).
12 valves
This is one of the variants of such power units, and so there were many more of them.
The reasons for this are the high mechanical losses since one shaft is used, with three cams per cylinder. There's only one valve at the outlet - it can't efficiently vent the gases, that was a big problem. 16 - The valve version turned out to be more efficient in terms of both fuel consumption and power.
As a result, this motor was removed in 2002.
20 valves
Five valves per cylinder are arranged here. At the inlet, they are "TRY". (also three cams on the camshaft), but on the release, "TWO". That is, as you may have guessed here, two camshafts are used, one driven by belt transmission and the other by a chain with a phaser. There were also variants with hydraulic compensators.
Again, because of the complexity of the design and mechanical losses, which did not give greater savings and power compared to the 16-valve version, they were removed from production.
24 valves
And that's what happened too, six valves per cylinder. One of the brightest examples was the HONDA company's development of the valves for its motorcycle, which worked - surprisingly according to the 4-stroke scheme, the code NR500. It was already in 1979. The engine was only 500cc and had oval pistons.
24 valves
The engine had 4 pistons (by the way, there were two connecting rods on the piston), its layout was V4.
Two connecting rods
As a result, it was spinning up to 16,000 revolutions and produced up to 100 hp, which is at 0.5 liters of volume.
BUT! The power unit turned out to be very heavy, complex and expensive, weighed about 20 kilograms more than other motorcycle engines of the time. And did not go into series.
There were also developments and the company MASERATI, but a lot of people experimented.
If you wonder how many valves in the internal combustion engine, you can find a lot of interesting developments, 10 or even 20-30 years ago, but not one option has not survived to our time, although it happened that they were produced quite a lot (remember engines HENDAY and AUDI).
The scheme "8 - 16" turned out to be the most persistent and the most correct of all. Although more and more old motors built on 8 valves are becoming a thing of the past, simply because the old, not powerful and not environmentally friendly motors are not. I think that in the end there will be only "16" left. Well, then there are electric motors.