I found a web site some time ago that described V8 firing orders and balance issues etc. Mainly about the old, traditional US V8s.
In one arrangement the cylinders fire unevenly, grouped into pairs. So you get two firing close together, then a gap, then another two close together and so on. This is what produces the characteristic burble of and old V8. It also caused problems on early engines with one big carb - the mixture was not the same on all cylinders because of the different time between cycles. So the first one of each pair got a rich mixture and the second was weak. Every other cylinder ran weak and overheated. Once the problem was understood the solution was clever plumbing of the inlet manifold (probably two plenums, I can't remember the details now). Of course, another solution is to use more than one carb, or even injection...
Balance is another issue. A V8 is never perfectly balanced, but it can be pretty good. The V angle is important, and there are two popular angles (what are they - I can't remember - 60 and 90?) Only a straight 6 can be perfectly balanced, and it follows that a V12 is too (it's two straight sixes).
Balance is in two parts - the simple rotating masses, and then the power strokes.
With a V12 not only is everything balanced but the power strokes also blend into each other, so it does not feel like an internal combustion engine. The power is delivered smoothly and evenly, like a big hand pushing the car along...
sorry, got off topic there
