I agree with all of this. But my question is why even bother repowering in the first place if you're happy with how it performs now and everything is running well. If something grenades, then do the repower, is what I would do. I love C18s and feel they're are great choice. Yes, you'll gain probably 3 knots and lose some fuel burn at cruise (85 GPH versus ?), but on the troll and 1000 rpms and under the Detroits are a lot more efficient than the C18's.....so depending on your usage you might not see any fuel gains overall.