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- 389 Block
389 Block
Pontiac V8 389 Block
Keep the Casting, Change Everything Else — 389 Block for Pontiac V8s
The 389 is the GTO-era block, and for a lot of owners keeping the correct casting in the car matters more than the last twenty cubic inches. Butler builds it as a modern short block without giving that up — the original block stays, the bottom end does not.
These Short Block Kits (SBK) use a Butler supplied 389 block and cover 395 to 454 cubic inches across three strokes. Each kit is a prepped block plus a balanced rotating assembly with your choice of flat top, dish or dome pistons. No camshaft, no heads, shipped ready to assemble.
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More About 389 Block
1. Three strokes, three displacements
The 389 uses the 3.00" main journal, and Butler builds it in three distinct stroke lengths with the rod matched to each.
| 3.750" stroke, 395-400 ci | cast or forged crank with 6.625" I-beam rods, supplied press fit and not assembled. The budget-friendly build and the closest to stock displacement. |
| 4.000" stroke, 421-427 ci | forged crank with 6.700" H-beam rods. A meaningful jump in cubic inches without changing the block. |
| 4.250" stroke, 447-454 ci | cast or forged crank with 6.800" H-beam rods. This is 455-class displacement out of a 389 casting. |
2. Piston choice and compression
The 389 kits are the ones where piston selection is genuinely open, and Butler handles it as a conversation rather than a dropdown.
| Flat top, dish or dome | you choose the crown, which is how the same stroke can land at pump gas compression or up where race fuel starts. |
| Head information required | add your head casting number or chamber cc at checkout and Butler confirms the compression ratio before the parts are ordered. Skipping this is how people end up with a combination they cannot run on the fuel they buy. |
| Total Seal file fit rings and performance bearings | rings are gapped to your bore during assembly, and rod and main bearings are performance grade. |
| Internally balanced | balanced as a complete assembly, which sets what damper and flywheel or flexplate the engine needs. |
3. Block prep and finishing the engine
Every 389 block is cleaned, magnafluxed, sonic tested, completely deburred, bored and honed with a torque plate, line honed with ARP main studs and square decked, with cam bearings and brass freeze plugs installed.
Not sure what your Pontiac needs?
Call our tech team at 866-762-7527. Tell us your engine, heads, car, and power goal, and we will put the parts together as one combination that works.