1979 to mid 80's johnson 140 whats the difference

[Ranger 330V]

okay this has probably been asked but I didn't see it...I have a 79 johnson 140, I was wondering what the difference is in those and the mid 80's I newer...I know they went to loopers and such...is that what made the difference in power?? I know pre 85 or so the engines were rated at the shaft and afterwards at the prop....what changes were made to give it the extra umph to get to a true 140hp?? was that when they went to the loopers?? did displacement change?? electronics?? exhaust tuning?? Just curious...thanks!!