Question about Mercury Racing motors?

[FormulaZR]

After reading the specs of all these engines, here's how I see it: the 525 and 565 are superfluous.

The 520 makes sense, and the 540 is a 520 with headers...so that makes sense as well. The 600 also makes sense for folks who really *want* a supercharger, and the extra power.

The 525 and 565 are not necessary. But even reading the Mercury site, they don't speak "well" of the 525 either.

The other thing is the 520, 540, and 565 (can't find specs for the 525) all have the same CR. The difference between the 540 and 565 is 10 CI (523 vs 533 cid) - although, the 540 is a large bore/shorter stroke than the 565, so if the 540 made the same specific horsepower as the 565, it'd be 555 hp. But, the 540 specifies 87 oct and the 565 specifies 89 oct; so I assume the 540 is slightly less aggressive on the timing.