Think about it, you ran rocket fuel for 1500miles, changed fuel and have now wreaked two pistons, so the underlying issue is likely to be one or more of;

High compression.
Weak mixture.
Too much ignition advance.

You can run whacky fuel and get away with a lot with all of the above, run the junk pedaled as petrol on the typical forecourt in the states and all three are critical.
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