why do early renix 4.0s make less power?

I just got a hold of a brochure for my 87 and I noticed that it had the outputs rated as 173hp and 220 pounds-feet of torque. I looked it up in my friend's Chilton's manual (The big ones that garages have that will cover say Domestic 1985-90) and it says the same thing, the 87 4.0 makes less than the 88-90 Renix which makes 177 and 224 pounds-feet. I've worked on my share of Renix 4.0s, and I never really noticed anything different between the 87s and the newer ones, so where do they get 4hp and 4 pounds-feet of torque?

Could be the tweaked the ECU a bit, I noticed the other day my 87 ECU and 88 ECU, have different data tags and part numbers.
May just be a missprint.

I blame the French Just kidding. 4hp and 4fp arent that much so it's probably just a minor evalution after a too rapid introduction. 4&4 arent much but I'm looking for them and many more on my 87 MJ; You can never have too much power.

Low self-esteem.

Injectors changed '87 to '88. Put '91 injectors in an '88 and see some fun! <G> Pass everything but the gas station!