Different HP motors with same blocks?

I am looking at moving up in HP for the new boat from my past, but I see people talking about motors with the same block at different HP ratings. Such as the Suzuki 115 and 140 motors. I looked at some motor performance documents and the results seem to be the exact same when comparing the zuki 115 and 140’s and also comparing the Merc 150 and 175 pro XS.
What am I not understanding here? Why would I want to pay more money for more HP when the results are the same?

the top end speed was the same and hole shot was the same? Something doesn’t sound right.

The suzuki documents were different, but they were on different boats with different gas levels, wind etc. But were pretty darn close to each other.

The Merc performance docs were identicle and the specs for the engine were also identicle. I figured the Merc documents were incorrect but it is why I was asking here. I am no motor head, so I do not really understand the “same block” statement.

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What am I not understanding here? Why would I want to pay more money for more HP when the results are the same?

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You wouldn’t. But then the performance numbers might not be all that accurate or really tell the whole story. I will tell you this though, in many walleye boats adding or subtracting 25 HP won’t have much impact on top speed. To get a little more speed out of a walleye hull you typically need to add a LOT more HP. Where you might see a noticeable difference is in the time to plane numbers or how a motor handles a heavy load in rough conditions but when it comes to top speed don’t expect dramatic differences when you’re adding or subtracting 25 HP.

In my opinion the best way to know for sure what motor is right for the boat you’re looking at is to drive a boat with that motor on it. Performance bulletins are a rough guideline on what you might expect and that’s about it.

as far as the same block thing there are a few different ways to look at it to increase horsepower that are block related. The easiest and cheapest is to just use different pistons and increase the compression (merc did this to bump the 50hp to a 60hp)
The next would be to use a crank with a longer stroke thus increasing the cubic inches hopefully resulting in more power.
Another is to cast different cylinder size into the block also resulting in larger displacement.

A good example is the small block chevy that came out in 1955, over the next 40 or so years chevy has had many different hp and displacements in the same block (from 260 to 400 cubic inches in the same block).

The marine industry uses other methods to adjust hp ratings on their motors. Mostly they use either intake tuning or exhaust tuning or both to limit horsepower. They may also use RPM limits. Using the same block for different horsepower is a cost effective way of making engines and is used industry-wide. Yamaha SHO engines are all 5.3 liter engines detuned to meet hp specs for different boats.
Why would someone pay more for a similar engine? in order to have the maximum motor for the boat and for resale later. There is not a reason beyond that if you want very similar results from a lower hp engine with the same block.
I could have had a 75 hp engine on my boat (instead of the 90 I bought) and would have noticde very little difference. That is, until I came to sell the boat and prospective buyers noticed that I didn’t max the hp on the boat. Now they ask themselves “Is the boat underpowered?” Unfortunately, there still are many boats sold that are underpowered and you only need to own one once and you promise yourself it will never happen again. You ask a very good question.