The four pistons used in the 2.2L are, from left to right, the 2724 with the wide pin boss (‘90-’91), the 2727 with the narrow pin boss, thicker head and higher compression height (1992-’93), the 2728 with a slightly smaller dish (1994-’97) and the 1998-’99 OEM version with the shallow dish.
There have been four different pistons used in this engine: From 1990-’91, the original piston was a Mahle 2724. It had the wide pin boss for the wide rod.
Both the piston and rod were changed in 1992. The pin bosses on the Mahle 2727 were moved 3.0 mm closer together so the small end of the rod was narrowed by about 0.120".
The compression height was increased by 0.1mm, and the crown of the piston was thicker to accommodate the 15% increase in horsepower.
The piston was modified again in 1994. The Mahle 2728 had a slightly smaller bowl (19.4 cc vs 21.8 cc) that increased the compression ratio for the new roller cam engine, and it weighed 16 grams less (312 grams vs 328 grams) which helped reduce NVH.
This revised, full round piston was replaced by an even lighter, slipper skirt design in late 1994 or early 1995.
The 1998 piston had a smaller dish, only .075" deep, to go with the new heart-shaped chamber.