I've written a little bit about this. For sure, it's complicated. I'll have to look back at the two pieces I did on the subject to try and give you guys a shorter, simpler version, though nothing about this is short and simple.
If you get a chance, check out the latest issue of Powerboat. I did a small article on the 8.2-litre engine replacing the 8.1 litre engine. The nut of it is ... the new engines, at least as marinized in the MerCruiser line, only make 5 hp more in the base and HO setups, but they do it as fully catalyzed models.
That's pretty cool considering that not all that long ago some of the biggest voices in the marine engine business were saying, categorically, that catalytic converters would "never" work in a marine application. Wrong.
But will they work in a big-horsepower marine engine? The people I've spoken with in the top two leading production high-performance engine companies are not optimistic. So where does that leave the big-horsepower engines? Well, as someone here stated, a builder's annual engine output does leave some wiggle room.
Not mentioned is averaging emissions, also part of the current CARB and EPA requirements, across an entire builder's line. That also leaves some wiggle room for engine models that don't meet emissions standards..
This certainly doesn't answer the question originally posed in this thread, but I hope it sheds some light.
