If you look at engineering curves for alternators----and they do exist, at least for Delco---- some LESSER rated output alternators put out MORE at lower / med RPM than some of the larger ones.
And as always---do some checks. Make sure your wiring is up to snuff. If you are running a trunk battery with a separate charging wire, no8 may not be large enough. Sure, it will charge, but it might not see full output.
