Re: Evinrude 75hp vs 90hp; what's the difference?
This question gets asked over and over and over and over and the answer is always the same. Every engine manufacturer has two, three and even four engines of the same displacement but with different horsepower ratings. Most of the time, especially with larger engines, there are relatively extensive changes between engines but on engines under 40 HP or so, sometimes its just a carb or restrictor plate change. One big engines though, timing, carbs, porting of the block, exhaust tuners, gear ratios, heads, and pistons (not bigger, just ported differently) are the main components. In those cases, unless you have a donor engine, it is not cost effective to make the change. Look at the car manufacturers of the 60's through the 80's. Chevy had a whole range of horsepower ratings for each of the various size small blocks. 350's were available with as low as 165 HP to well over 300. Cam, compression and carburetion are the key components. Head design was another factor. The same applies to two-strokes but there are no camshafts.
The only way you will know what needs to change on your engine is to compare parts lists -- including the block P/Ns as they will carry different numbers if they are ported differently.
