all that is changing now.

if you had a car that ran nice and cold, but its main operating spec was climbing a hill while towing a trailer for 4 hours at full throttle and emissions were not a concern... that's how you'd tune it too. like a big RV. a bit rich, and conservative timing.

the new marine inboards being sold are mandated to have cats, even with wet exhaust, and they are (afaik) mandated to have NB o2 sensors aiming for stoich during cruise conditions.

NB o2 in a wet exhaust system is a nightmare, no matter which part of the pipe you put it in, you really need to build a trap system for it so it doesnt get soaked. honda did that with their outboards, and so did some of the yamaha 2-stroke stuff, and they were always the first thing to die, even with elaborate systems to avoid just pouring salt water over them. scary stuff, but good for a skiboat, once its on plane, it's pretty efficient, so stoich would be a good thing.

im not even sure what they've done to mefi controllers to deal with it. we aren't getting stuck with them in canada until next year, but im curious to see how they figured 'er out. increases the price of a new boat by a couple grand apparently, since the cat plumbing is expensive stuff.