Originally Posted by woolf
Attached the spec sheet for the APS 55i we installed.
Thanks. I hadn't heard of APS before. It's a bit hard to tell, but they seem a bit like Balmar, packaging up stuff for specific applications. My guess is that like Balmar, they are more or less stock LN alternators. Their 42i sure looks a lot like mine... Nothing wrong with that, just not likely to yield any magic with respect to efficiency.
Interestingly, their "large frame" alternators are 50% efficient, your 55i is listed as 87%, and the 42i is 70%. That's quite a spread. I also expect the efficiency number in the data sheet is best case since it is otherwise unqualified.