The more air you can fit into the engine to more power you will make, the 4 cylinder engine is just half a V8 so you can't say one engine is better than the other since they are the same thing, the V8 has a few design advantages though as far as being more compact that two 4 cylinder engines and sharing a manifold etc. Also the more cylinders you have the smaller and lighter you can make the pistons and then you can make everything spin at smore revs without breaking and the more revs you can spin with more power strokes per/time you can make = more power, take note of forumula one, 18,000 revs buys you alot of power in a tiny little V8.
Thats also why as far as out and out performace goes even though they are more efficient no four cycle engine can match a two stroke or rotary engine of the same size and revs, because they are firing more often. With a turbo even with a small amount of PSI (boost) you can easily fill the engine with 150% of the total air capacity of the engine so you will make more power but that said the 4 cylinder and 6 cylinder engines are inferior to the engines with more cylinders, it's just that they have alot less parts and are cheaper to make so will allways be more common and as they don't make alot of power with a turbo you will see them turbo charged more often. But in your top of the line models and high end sports cars, complex V12's and the like are common.
And back to the original question of why a turbo 4 or 6 can pound a V8 on take off, most V8's from the factory are designed to be a slow long lived engine that can do alot of hard work without breaking. They send them out with mild tunes, mild camshafts, restrictive exhausts and usually in very heavy cars