That but most of all how the crankshaft differs in the two engine designs.
In a Ferrari the crank is basically a 4 cylinder crank where two connecting rods sprout from each lobe.
In a Chevrolet smallblock the crank has a lobe for each individual connecting rod.
By using the doubled 4 cylinder crank the Ferrari V8 revs smoothly like a 4cyl would, by having an individual space for each connecting rod a Chevy sounds lumpy and uneven when each cylinder fires.
They're both even-firing engines. The difference with the cross-plane crank is that
each bank of four cylinders is uneven firing, just like the 2009+
Yamaha R1. I.e. the order of firing, in terms of cylinder banks is, for example:
L, R, L, R, R, L, R, L
This was actually perceived to be a drawback to the design, but most people love the resulting sound.

The flat plane has an ignition event following in the opposite bank every time (i.e.
L, R, L, R, L, R, L, R), so does tend to sound like two synchronised / interlaced fours.
The
intake sound of a flat-plane V8 is unique, and not really comparable to the ordinary
straight four, and is only superficially tonally similar to the
cross-plane V8.
As for smoothness, the cross-plane wins hands-down, whilst the flat plane has a tendency to vibrate (assuming both engines are using a fully counter-balanced crankshaft, which isn't a guarantee on old cross-plane V8s...). That's why Yamaha went with the cross-plane in their MotoGP bike, as per the video I linked above.

The effect is less severe with the flat-plane V8, owing to the V-angle, but is still noticeable as a vibration.
I notice the NASCAR cars sound as they did at GamesCom, and it's a shame that R8 vid is such a mess. Still, keep 'em coming!
