The OP has not been around since September of 2024.. so perhaps we will never know if he corrected his issue.
The AR190 uses the normally aspirated 1.8L.
Here is what I see right up front, he was running fuel that is 6 points higher in octane that what the manual calls for, which I believe is 87, but could be 86 like mine. Contrary to what some may believe 93 and 87 octane have the same amount of btu’s per gallon, but the 93 burns slower in an engine that does not require it as the cylinder pressure is lower than an engine that has higher cylinder pressure whether by mechanical compression ratio, or forced induction like a super charger. Running higher octane fuel in an engine that does not require it actually lowers horse power and creates higher heat in the cylinder as the burn of the fuel is so much slower it continues to burn past 60* of crank rotation, chasing the piston down the bore. Running iridium spark plugs in an engine not designed for them just creates more negative cash flow, and may not last as long as the oem plugs.
The OP said he lives in OH so altitude shouldn’t be a factor, not true, if it is really hot and really humid it will raise the density altitude and affect horsepower. I checked Columbus OH, altitude 780’ on a 95* day with a dew point of 70*, that raises the density altitude to just over 3500’, and a 10% power loss. Having said that, the OP reported 7450 rpm so that wasn’t necessarily the issue unless there was some impeller damage and the impeller was not fully loaded.
You can check your own locations density altitude by using this online calculator
density altitude calculator for pilots
www.pilotfriend.com
Since we can’t ask any questions.. I’ll answer yes, sludge build up on the bottom of the boat can dramatically affect the boats overall top speed. We also cannot ask; how much fuel was in the boat, how much cargo / people weight-this is huge, where was the people weight if any located?, what was the sea state, oil level correct?, impeller clearance good?
I’ve also seen people who were testing the lucky 13 cone report top speed loss.. so not so lucky on that front, but they alleviated some cavitation issues.. everything is a compromise you just have to find the one that suits your situation the best.
As far as the impeller goes.. just having a solas impeller doesn’t mean much, what matters is what the pitch and blade shape were and how is the gap between the impeller and the wear ring. It is possible the solas impeller the OP was using was under pitched or underpropped and he was on the rev limiter. Again, no way to ask a question, why did you put a Solas impeller in the first place? If the reason was it was over pitched / over propped and the rpms were below rated rpm, and the impeller was purchased to raise the rpms then the jet pump will not pump the same amount of water at a given rpm. I boat at high altitude, density altitude in the summer can get above 9000’, so I got some different impellers and had them pitched for high altitude use, I got a lot more performance at the cost of roughly .3-.5 mpg, but my top speed increased dramatically, from 29mph in some cases to upper 30’s, and even 41 in other cases.
As you can see, there are a lot of questions to ask when a lot of the relevant information is missing that can affect top speed.
