That seems to point to Alfa’s quality control problems and not an inherent flaw in the concept.
If engine sound is your only concern, you can get that V8 rumbling from a 4 banger by splitting the exhaust manifold. Instead of a single 4-2-1 or 4-1 manifold, you can use two 2-1 manifolds with slightly different pipe lengths. I’ve heard it is very effective!
The two main advantages that can be gained through having more cylinders:
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Better balance, and so less vibration. This has become pretty irrelevant these days, with better understanding of the problem, more experience, etc. Vibration from a big 4 cylinder Toyota engine, for example, is a lot less than from a 1970s vintage V8.
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Shorter stroke. For a given physical engine length, if you double the number of cylinders from 4 to 8, you can keep the bore pretty much the same and halve the stroke. This halves the maximum piston speed for any given rpm. Assuming you’re using similar materials for both engines, that would allow the V8 to safely achieve double the rpm. So your 7,000 rpm redline 4 cylinder could go up to 14,000 rpm in V8 configuration. Torque is proportional to engine capacity, but power is proportional to both engine capacity and rpm. The 120 kW 4 cylinder engine could be turned into a 240 kW V8. This is precisely why Formula 1 engines, which are of limited capacity, tend to have more than 4 cylinders. But Joe and Jane Public tend not to like running engines in “screaming” mode. It’s better from a marketing perspective to just stick a supercharger on the 4.
That should read “For a given engine capacity and physical engine length”.