Here is more food for thought. Not advocating one way or another for using 87 over 91. The compression ratio on the 112/113 is 10:1 I believe. Just because I am curious I looked up the engines that GM puts in the Sonic and Cruze (we used to have several of these as company cars) and they call for 87. Those engines are 10.1:1. I just wonder how it is that GM engines use 87 with the same compression ratio as the MB engines. Maybe they leave their timing retarded all the time.