OS2U-1 & OS2U-3 make no sense

I’ve noticed, while playing the game that I own both OS2U-1 and both OS2U-3, the weirdest part in them is the engine, they have different engines, however the same amounth of horsepower.
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So, as you can see, they’re the same. But my question is why is the OS2U-3 climbs faster with the same engine and same modifications as maxed out ? It climbs 2.2 times faster than the original WHILE its heavier, so why is that the same plane with same engine horsepower and same airframe can climb 2.2 faster while being twice as heavy too ?
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These statistics makes no sense but correct me if im wrong here.