You do not need to do head work for an over bored cylinder. The bore of the cylinder doesn't have much to do with compression. Not to mention, unless the high octane fuel isn't available to you, you can always just up the octane of your premix. I have head work done for higher compression, and I have to run 110 octane minimum to avoid pre-det. You should run a minimum of 93 octane (available at most gas station, at least around where I live) for the rm80.