In response to your original question, I ran 87 M+R/2 Octane gas on my stock '76 MG Midget (1500). The previous year, '75, as well as '77 on vehicles had dished pistons which had 7.5:1 compression. Now, I ran regular US 87 without problems at 9:1 stock compression (at least when compared with the fact that I had a monstrous racket from the need of a rebuild ... I believe it needed a gudgeon pin on a piston, and that was the reason for the racket). At any rate, I went to 10.5:1 compression and the rest of engine tuning and now run Sunoco Ultra 94 with no problems (at least not engine related ones). I have other problems, but they're not due to engine problems, instead a nagging clutch issue which I expect to solve around Christmas (I sure hope so ...). Hope this helps!