Have you changed the piston pins or you are still on the stock NA ones? I'm sure you already know this, but IIRC, they are the weak point on the turboed NA engines.
'90 Blue Nissan 300ZX Twin Turbo '91 White Nissan 300ZX Twin Turbo '93 Blue Mazda RX-7 R1 Twin Turbo '90 Black Nissan 300ZX Naturally Aspired (SOLD - 08/23/05)