I understand DI and it's efficiencies, but I don't understand how you could have 11:1 and not knock with 87 octane. Even turbo's are limited to about 3 lbs of boost and all sorts of timing retardation to boost at 3 lbs and not ping. A turbo with 8:1 pistons limited to 3 lbs of boost is all just to get more air/fuel into the cylinder to mimic a higher cubic inch engine. To increase efficiency, you need higher compression ratio's. 87 octane,( to my knowledge) won't do that with 30lbs of boost on a 8:1 or even nat aspirated @12:1 compression. You will burn a piston. Water injection might help to a certain degree.
This is what I miss so much about the "Good Ole Days" and 102 octane.
Do these GM engines have variable valve timing or something? What cars have these? I'm interested.