J-Body History by Generation
The 2.8 liter V6 engine was found in all Z24s in the years 85-89. In 1987, the 2.8 was slightly redesigned for better leak control for the 88 model year. This engine produces 120 - 130 HP @ 4800 rpm and 155 ft.lbs torque at 3600 rpm.
Generation 2Phase I
The second generation began in 1988. In 88 and 89, the Z24's still had the 2.8, but from 1990 through '94 the Z24 got a 3.1 liter V6, basically a stroke out version of the 2.8. In fact, the 2.8 and the 3.1 share all parts except for the crank and the pistons. The 192 ci. 3.1 V6 pounces the ground with 140 HP @ 4500 RPM and 180 ft.lbs torque @ 3600 RPM. In 1992, GM was able to get the power peaks lower in the RPM range so HP and torque readings were at 4200 RPM and 3200 RPM respectively. In 1991, there were a few revisions made, including the ground effects package and the interior. So 1991-94 became the "Phase II" 2nd gen, while 1988-90 was the "Phase I".