[PAUL K]

One needs to consider the intended use of the block. A fellow that worked for me bored out his Olds 400 to 455 bore size. It left the bores dangerously thin. Yet it took 23k hard miles before the cylinder cracked and hundreds of dragstrip passes. This engine was making around four hundred horsepower. At seven hundred it wouldn't of lasted nearly as long.

[RA66GTO]

I'll be the guy in left field.
For a "just get it running" build we took the original 66 WT 389 to +.090. Loaded it with SpeedPro forged pistons, King bearings, a Lunati Voodoo Roller Cam, Cloyes billet timing set, KRE 74cc heads, Melling oil pump, fuel injection, Canton pan, etc.
Intended as a "Temporary" engine, we now have nearly 30k miles on it. Primarily used for long distance touring.
Temp stays around 190* on a hot TX summer day, may creep to 212* in traffic with the AC on.
Goal is build a MR-1A to 433 with a 4.00 stroke, yes it will have to have custom sleeves.... one can dream...

[PAUL K]

Originally Posted by RA66GTO

I'll be the guy in left field.
For a "just get it running" build we took the original 66 WT 389 to +.090. Loaded it with SpeedPro forged pistons, King bearings, a Lunati Voodoo Roller Cam, Cloyes billet timing set, KRE 74cc heads, Melling oil pump, fuel injection, Canton pan, etc.
Intended as a "Temporary" engine, we now have nearly 30k miles on it. Primarily used for long distance touring.
Temp stays around 190* on a hot TX summer day, may creep to 212* in traffic with the AC on.
Goal is build a MR-1A to 433 with a 4.00 stroke, yes it will have to have custom sleeves.... one can dream...

Good info, thanks for posting.

All-Pontiac offers smaller bore sizes. We use them for Super Stock builds.

[Sirrotica]

Anyone that is skeptical about the 65-66 blocks not having as much material as the earlier 389 engines. There is documented proof that the 65-66 blocks are possibly inferior in the amount of iron used in those castings compared to earlier castings. Having had one .060 over bore fail due to weak cylinder walls I would at the very least sonic test any of these blocks before boring one more than .030 oversize. Since there are other options for stronger castings, 65-66 would be my last candidate for a .060 overbore without a sonic test.

Thin wall casting blocks can lead to reduced durability in the Pontiac 389 engine, as they may be more prone to overheating and cracking under high-stress conditions. This can result in a need for additional modifications or repairs to maintain engine performance and longevity.

Impact of Thin Wall Casting on Pontiac 389 Engine Durability
Thin Wall Casting Characteristics

Material: The Pontiac 389 engine features a cast iron block, which is generally robust. However, some blocks, particularly later models, may have thinner walls.

Wall Thickness: Thin wall castings can lead to reduced structural integrity. This is particularly concerning in high-performance applications where stress and heat are significant.

Effects on Durability

Overheating Risks: Thinner walls can lead to overheating issues. The reduced material may not dissipate heat effectively, increasing the risk of engine failure.

Cylinder Wall Integrity: Thin walls can compromise the cylinder's ability to maintain proper compression and seal. This can lead to oil leaks and reduced performance.

If you consider boring one .060 without testing it, I'll default to Clint Eastwood. famous line in the movie Dirty Harry

Ya gotta ask yourself one question, Do you feel lucky???

[Gary H]

Originally Posted by RA66GTO

I'll be the guy in left field.
For a "just get it running" build we took the original 66 WT 389 to +.090. Loaded it with SpeedPro forged pistons, King bearings, a Lunati Voodoo Roller Cam, Cloyes billet timing set, KRE 74cc heads, Melling oil pump, fuel injection, Canton pan, etc.
Intended as a "Temporary" engine, we now have nearly 30k miles on it. Primarily used for long distance touring.
Temp stays around 190* on a hot TX summer day, may creep to 212* in traffic with the AC on.
Goal is build a MR-1A to 433 with a 4.00 stroke, yes it will have to have custom sleeves.... one can dream...

I've done the same thing. We had a 66' 389 block and some .060 400 pistons. Had it sonic checked and it was good to bore. I was really surprised!