YES! There's a lot of possibilities, it depends on what you plan to do. Also on the water the hull is a major factor in performance but there is plenty of powerhead and lower units modifications available if you have the cubic dollars.
Many years ago I had a friend who was into boat racing. He ran big block engines but when I would hang around I would see all sorts of stuff. Lots of people ran modified outboards. One such class of boat racing was the enduros, where they would typically be 9 hours of racing on a fairly small oval course.
The outboard boats that dominated this class were based on a "pickle fork" hull but instead of being really low profile they had a rather tall cockpit followed by an enormous gas tank. The outboard was modified quite a bit. The lower unit was typically stripped down, gear shift removed so it only had forward. I believe that the water pump was also removed and replaced with a water pickup tube sitting behind the prop. Dry exhaust system with an expansion pipe like a dirt bike would have.
These boats could barely get on plane with a full tank of gas, but once they did they would just scream! Some boats even went as far as having an airplane style rudder so they could steer whey they started "prop walking".
Believe it or not, I actually did that exact same search with that exact same phrase and, you guessed it, got the exact same results. Those results did not satisfy my curiosity so I figured id post on here to see if anyone has and experience with it first hand.
Patman, the outboard is a 25hp merc and the boat is a home built mini hydroplane. The motor has nothing done to it right now but as is, it does 40mph. Id like to get a little more out of it with a more agressive prop for top end but I dont want to lose acceleration so I would like a little more hp. So I am looking at engine mods.
there are generally many possibilties- ??
but that depends on the exact engine?
as example i modded my johnson 90 outboard years ago..
the 125hp heads etc fit on, with very minimal work..
if i already had a 125 ,, it could be modified,, but not with easy bolt on stuff like the 90..
but almost all the common outboard engines have a lot of potential in performance, as they are built with longevity/reliablity in mind and not shear hp.
just like the typical 2 stroke dirt bike engine.
so there is often a nice balance , IN BETWEEN, you can find if looking for more performance..
my boat isnt fast really, but does about 58 to 60 mph.. (GPS'd) as the speedos are always off..
which is fast enough on the water..lol
freshly wax the entire hull , and it gains about 3 mph.
Check out screamandfly.com for a starting point. They might be a bit more in to the large displacement engines but the knowledge base there is good and they might be able to point you at something a bit more specific for the smaller OB's.