I have not tried to run 89 octane because I am "on the edge" so to speak of being able to successfully run 92/93 octane. But I built the engine knowing that would be the case. It has a .039 quench area, AFR 190 heads, a CompCams 280 Magnum cam, Edelbrocks RPM intake and 750 carb. I a very satisfied with the performance and its street manners.