I just had a 69 4 bolt 428 block sonic checked. It is already .070 over, it needs a sleeve and I will take it to .090. On the major thrust side it ranged from .210 to .220 on the minor it ranged from .185 to .195. I have taken a few of these to a 4.210 bore. Sonic check will know for sure. I think Probird had one a 4.250.
This block was a GME casting.
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66 GTO Nostalgia Super Stock/Street Legal Car
421 CID, stock block, Wenzler Intake, 2- Carter 750 AFB's, 3.90 Gears, Full Factory Interior, Full Exhaust, Stock Suspension 3750LBS 9.77@136.99
Multiple NSCA/NMCA World Champion
66 GTO 389 3x2, 4 speed, 4.33 gear, Montero Red 33K original Miles
67 GTO 2dr Post, 428, Tri Power, 3.55 Gears
80 Trans Am Black SE Y84 W72 WS6
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