I have a 4.155 bore 393cid 18-degree SBC. Heavy (42 pill in fogger) NOS. I put about 10 nitrous runs on engine and it started smoking. Pulled head expecting damage from lean NOS tune up, but found the pistons in various stages of damage, looks as though the ring land is flexing and breaking at perimeter where it is thinned for the intake relief. It has a 2.20 valve so it really crowds the edge. What can be done to prevent this from happening? Rings are dropped .29 inches from face, gas ported JE flat tops. Need help, I'm afraid it will ruin another $$$ pistone set.