I order of your responses;
He did not have to refuel. His mother left him a full tank of premium. She only uses speedway premium.
We never heard any spark knock. After removing cylinder heads, I found no signs of parts in cylinder.
No modifications, YET, I did remove the catalyst media from catalytic converter.
After I removed it the engine developed a miss in one cylinder for a couple of minutes. I revved it and it went away, till now. I think the end of the spark plug wedged between the exhaust valve and the seat, starting the burning process.
Received a call today from the machine shop, said head was cracked in that cylinder and one next to it. Found one for $70, will pick up and have valves ground with other head.
Is this when I change supercharger fluid???