Ok, now for the correct answer to your question.
A 12 valve head will use 2 valves per cylinder on the intake side and 1 on the exhaust side. As fuel is sucked into the engine on it's own having a greater surface area of two intake valves is advantageous. The one exhaust valve is sufficient due in part to the piston forcing the exhaust out.
One valve is always a bit heavier than 2 light ones so the 12 valve head may spin a bit slower and offer a bit less performance as well as having different intake dynamics.
A 16 valve head will have 4 valves per cylinder and typically the intakes are of larger size then the exhaust again for the same reasons.
Fresh mixture is sucked in while exhaust is forced out so it's desirable to have larger intake valves. The 16 valve head will be able to spin a bit more due to slight reduction in weight of all the valves combined.
The differences between the two heads would be the ability for each engine to develop power at a certain rpm. and the number of camshafts. 12 valve heads and some 16 valve heads use only one camshaft but 16 valve heads typically have two camshafts.
Performance engines are typically a 16 valve setup. Audi and Yamaha made 20 valve heads for their 4 cylinder engines buts gains were minimal so they have gone back to 16 valve heads.
Hope this helps.
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