I have a Mercury 30hp Four Stroke and I was wondering what the difference between the 40hp and the 30hp motor, from the specifications on their website, the enginges of both motors are identical. I was wondering where the extra horsepowers come from on the 40hp motor. Can anything can be modified on the 30hp engine to give it 10 extra horsepowers, and if so how much would it cost?<br /><br />Thanks