.if the head and the clearance is designed similar to its smaller displacment counterpart a significantly larger bore will usually add some static compression because theres much more squish band and crown area on the piston to match ,theres lots of complicated theorys on why it will do this fully understood by men smarter than myself ,but the best way to describe it is the trapped volume is critical but it works in unison with the squish band width to favor certain rpms and torque ratings in the powerband and really the same can be said for the squish clearance ..even the dome shape is important .increase the bore you ll generally get more squish band area evne if the clearance is the same .i have seen this personaly many times on comparing small and big bore banshees and blasters of similar setup .2stroke porting can never add static compression ...only reduce it. does this by increasing the port duration and drasticly increasing the given port area above BDC theres less time and area (cylinder wall) for fuel to be used before it has to ultimately exit ,it varies but usually on decent sized bores it can decrease compression by 5-15 pounds depending usually on your exhaust port height and shape ,also as far as what constitutes detonation and requires high octane rating is much more than just the static compression. it was a very informative article on how stuff works .com but unfortunatley its not entirely accurate especially for 2 cycle designs.the main things that will effect detonation and the need for race gas are ,static compression ,exhaust port height and area the ignition timing and spark voltage ,squish clearance .high octane rating (makes more sense to say anti -detonation rating) race gas burns slower and allows the fuel time to be compressed and burnt instead of ignite and explode the piston down too soon out of sync with the stroke/ignition timing and thats why you hear an erratic knocking sound ,your engine doesnt know if its coming or going lol and that concetrated area on the piston over time and the thousands of explosians will melt away the aluminum due to intense heat and burn a hole directly through the top of the piston and/or causing a seizure,this is why on engines that are detonating youll usually see little white flecks scattered over the porcelin and it will look whiteish ,thats actually aluminim from your piston being compressed destroyed and melted ,not a good thing !