Hi guys, I'm still a little unclear about the 401 and 425 blocks. Are the 401 and 425 blocks exactly the same but the 425 was bore larger at the factory? If so why could the factory bore these blocks and yet everyone advises not boring the 401 to 425 specs? Cheers, Gary
Some of the 425 blocks had the sand core for the water jackets"shift" during casting and cause thin cylinder walls in the front and rear cylinders depending on how it "shifted"......fully over half the cars that i've had in the last 30 years that should have had 425's did NOT have their original block...they had 401's......probably 20+ cars. If you are gonna build a 425.........have the cylinder walls ultra-sounded for thickness....... Buick used a thicker iron for the 425 blocks because of a porisity problem in the cylinder walls........ Peace WildBill
