I hesitate (for just a second) jumping in here. Boatdiesel was the primo source for information on recreational and small commercial diesels. Then Tony Athens, who is an extremely knowledgeable guy, had a falling out and started his own site at sbmar.com/community mostly dedicated to Cummins engines. I subscribe and frequent both.
Unfortunately or fortunately for boatdiesel, two of the best Cummins guys: Ski in NC, who posts on this forum, and Paul Foulston, an ex Cummins UK development guy, didn't make that trip and stayed with boatdiesel only. So the Cummins expertise is split between the two forums. Also Tony no longer posts a lot on his own site. Rob Schepis does and he certainly is qualified.
So if I had a Cummins engine I would visit both sites and probably would not subscribe to boatdiesel as Tony's site has tons of Cummins info, but not much on other engines. But if I had a Yanmar, Volvo, Cat, Perkins,.... I would post to boatdiesel and probably spend the $25 per year membership fee so I could use the on-line calculators and access their pdf library of engine datasheets and manuals.
David