I see guy's on here all the time adding a "few" HP to their motor. Not a new motor, maybe just a few HP picked up in some better parts in a rebuild, etc...
How does this affect the insurance if it was previously a bone-stock build? I'm talking maybe a cam change, or a carb change, minor things. Maybe only affects the top speed by a few mph than what was stated in the declaration, maybe doesn't even raise it. But the HP rating is higher if dynoed?
I'm not talking about a 600+HP monster, I'm talking about smaller HP with mild increases - think of a 370 bumped up to 420, or a 330 bumped to 380 with internals, and modest externals (carb, intake, exhaust...)
What's the take on this??

Alot of insurance companies have a 500HP limit or a 75 mph limit......neither of your senarios are likely to affect those limits. If we're talking something that changes top end 2-4 mph I don't it would matter. (what's the difference in hitting something at 63 vs. 67???)

As long as it looks stock you will be OK. They are not going to dyno an engine involved in a claim.

That's what I'm thinking too. I guess my question is "how far will the ins. Co. go to get out of paying a claim?"
We all know, so little as changing a prop can change a top speed, and minor motor enhancements can change HP, but to what enth degree is the insurance Co. going to investigate in the event of a claim, and upon investigation, how much of a tolerance/variance level acceptable? When I signed a policy, I was asked to state a HP, and top speed. The HP is the stock rating, and the MAX speed - I don't know, I've yet to run the boat - estimate 65.
How will that hold up??

As long as its not real obvious that increased hp by a lot, I wouldn't worry about it.