Originally Posted by Gulfislander
To me it seem to be related to the prop pitch...maybe the engine does not have to work as hard?? I just worry I may be damaging the engine.
By far, the change in prop pitch is the most likely culprit since that's what changed. Your change in RPM vs speed confirms that the pitch is different, but from what you describe (boat moves faster at same or lower RPM), the engine is working harder, not less. It has to produce more HP at lower RPMs to make the boat go faster than it did before.
Whether the engine is overworking, I don't know. On power boats the test is to confirm that you can attain full rated engine RPM, preferably a few hundred RPM more. That tells you that the load from the prop matches the output capacity of the engine. If you can't hit full RPM then you are over-propped. I can't see why that test shouldn't apply equally well in your case, and it's real easy to do.
Regarding the smell, your exhaust should smell like diesel - that's pretty obvious. I'm not sure how you would tell if it's the visible gas (steam presumably) or the invisible gasses in the exhaust that you are smelling. So the smell may not tell you much. Is it noticeably smellier than before? More smell would actually be consistent with the engine being more heavily loaded. If you are getting black smoke then you are definitely over-propped, but it doesn't sound like that's the case.
I'd do the full-RPM test and take it from there. Everything points to this simply being steam in your exhaust. As long as you are not over-propped with the new prop, I think you are good to go.