318 MAX fuel economy builds?

Every engine combo is different. Will it detonate with 9:1 CR? Who knows, it might. As you increase CR, the power increase becomes less. It is NOT a linear curve. So you will have to decide whether increasing the CR is the worth the risk of detonation. A lower CR will allow you to use a lower octane fuel if it is available in your area. This might save you more $$ than going to higher CR that requires more expensive fuel.