[Jac Mac]

While it could be just a bad batch of fuel, the possibility remains that part of the damage had already occurred on the previous run and the 'pinking' was as a result of the damaged piston causing preignition from the broken area/exposed ring/ & oil in the fuel mix.

Pay close attention during teardown to the following- Look for detonation signs on plug porcelain , wrist ( gudgeon ) pin for partial seizure in piston pin bores [ this causes piston to 'tip' in the cylinder and unseat the rings which allows oil to get in the fuel mix where it lowers the effective octane rating ], condition of top bearing shell in conrod [wear and has it still got 'crush' & and a 'snap' fit in rod], any sign of 'fretting' or movement of main bearing caps or main brg shells.

Also during the fuel stop an airlock might have developed in the cooling system from 'afterboil' or heat soak which might have created a hot spot in the water jacket during the next run.

You may have a 'dynamic airflow' issue at speed which favours one ram tube more than others creating a lean out, or in some cases where one cyl fires immediately before its mate and robs airflow. Airflow around the drivers helmet can also play havoc.

Was the motor built specificly for its purpose? or have you simply used a 'crate' motor without any attempt to blueprint or check vital clearances etc.

With detonation a lot of the above fall into the 'what came first-the chicken or the egg?' category-- thats why you have to look hard at what happened in the runs prior and also examine the engine parts on teardown very carefully. The fact that you did not experience any problems on the dyno means little once you start to factor in stuff like airflow at speed and cooling etc. If you find definite indications of most or all of the above signs, consider the motor a throwaway, it will be nothing but trouble from here on if its really had an extended run in this state.