So I got a hold of some vintage BMW accessory pistons. According to a Feb 17 1992 Autoweek magazine clipping I received as part of the original sale, they pumped the compression up from 9 to 1 to 9.5 to 1. The article(written by William D. Siuru Jr.) also says they were part of a "dealer-installed performance package" that boosted power from 40 hp to 55hp. The kit also included carb modifications and dual exhaust. I sent the pistons to Swain Tech Coatings and had them coat the domes with a ceramic heat reflecting material and had the skirts done with a molly impregnated coating to reduce friction. I took some side by side pics with the OEM sport coupe pistons. You can see that they are slightly taller, use an extra compression ring and have a taller dome with valve relief pockets on it.
