Well from personal experience now, DONT GO PAST 9 PSI if you are not ready for a rebuild. TWICE now i have cracked piston ring lands with good to perfect tuning. The first time was somewhat hard to dertermine what exactly caused it. I still think it may have been detonation, but if it was, it happened at 10+ psi. This was with 93 octane fuel, but may have run a hair lean, which is what i will account for that time. This last time, this past weekend, i was tuning my fuel pressures again when i went to a higher rise rate setting on my fuel pressure regulator. Every thing was perfect- WOT in 4th gear, 10.5 psi boost, egt's were no more than 1500 degrees, plenty of fuel pressure, and o2 voltages were .96. The car did not detonate at all(detonation will crack stock pistons without a doubt). The car was fast. Very fast. After that 10.5 psi pull, came to a stop, and the car idled off, and 2 hg's less in vacum. Pulled the oil dipstick, and puffs of vapor were coming out. Low compression in #3 cylinder reveals the damage- cracked piston ring land. The stock pistons will not tolerate detonation, and high horsepower outputs. Peroid. If you are willing to push the edge, like many of us, and are fully aware that you will need to rebuild in the near future, boost away!