I have had nothing but big blocks for the last 9 years, and not a single one that was built up a little, or a lot, would run good with any less than 18* initial. (without vacuum of course) You still want your total at 38*. You shouldn't have detonation problems with 11/1 and hi octane fuel, so there must be something else happening. What's your dynamic c/r?? What are the cam specs?