Basically, what is the advantage of extra cylinders?

Compare an eight-cylinder engine and a six-cylinder engine. They both displace X liters (say 4.0). All else being equal, which produces more power? More torque? Is it the same?

On first thought, more = better. But wouldn't an eight-cylinder engine have more moving parts, and therefore higher internal friction? Do two engines of the same displacement theoretically use the same amount of gasoline - say for a really big six cylinder engine, each cylinder firing once = 1 gallon used. For a really big eight cylinder engine of the same design and displacement, would it also use 1 gallon after each cylinder fired once?

Sorry if my mind is just being retarded

Not having to replace a turbo or blower...

One advantage is balance. Each piston/rod pushes the crankshaft only a short distance, so having fewer of these means power "surges." Many 4 cylinder engines even have balance shafts to offset this effect.

With enough cylinders, there is  an overlap of the power produced by each -rather than a lag.

To many factors to make a blanket statement about horsepower/torque, however most 6 cyl will turn more peak RPM  than an 8 cyl for the reason you did mention (less moving parts). I am sure someone  (KeithJ) will be along to provide some accurate info.

It's complicated.

The short answer is that not all aspects of engine performance scale linearly. That is to say that doubling the number of cylinders doesn't necessarily double some other parameter- it may triple it or some other ratio. Of course this also apply to negative parameters as well- more cylinders can have a negative or positive influence, so more is not necessarily better, depending on your design goal..

My guess is that cylinder count in a car engine is usually determined by a couple of chief factors- cost, overall engine size, weight, balancing forces and torque/power curve desired.