what happened to the 4.0 between '88 and '89!? 27 more HP?!

Okay, I knew about the change to the HO in early 90s, but the '88 and '89 are both running the Renix system. My Chilton's manual says the '88 puts out 150 HP and 210 lb/ft, but the '89 puts out 177 HP and 224 lb/ft.

27 HP and 14 lb/ft! that's a pretty big difference, almost a 20% boost on HP.

So what did they change? and more importantly (and why this is on the Mod Tech board) is how do I change my '88 to the '89 stats?

Misprint. The '88 thru '90 were all 177 HP / 220 ft-lbs torque.. 1987 was 173 HP / 220 ft-lbs torque. Increased to 190 HP in 1991, when it was designated as the HO (High Output) engine.