11.5 and open chamber iron heads will never work with pump gas; especially with contaminates in the chamber. I don't go any further than 9.5, with quench pistons, in open chamber iron heads and pump gas; but I do use shorter cams. I use 84cc alum heads with 9.8 pistons in one of my drivers with 93 octane pump gas and have zero issues. I really like this combo, but I don't chase every last horsepower either. my thoughts on the 9.8 engine was to allow for some carbon build up which should put me well over 10:1. there are many factors to building in detonation resistance (no such thing as detonation proof) into an engine.