I don't know why. But I will say that I've run a stock n/t block with stock 7.8 turbo pistons for a LONG time with no issues. Before water injection, with the 16g sh!tting itself being pushed. Then with a 60-1 with over 48lb/min recorded. I wouldn't worry too much about it.
Of course, a winning lawsuit will net you some forged pistons which definately don't need the extra cooling
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Matt
Bolton Holset H1C w/ external gate, fp2X cams, DSMLink, 3" exhaust, FMIC, water injection
"There is nothing better for man than to eat, drink, and see good for all his hard work." Solomon