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389 Blocks (395-480 cu. In.)
Pontiac V8 389 Blocks (395-480 cu. In.)
Three Roads Out of a 389 — 389 Blocks (395-480 cu. In.) for Pontiac V8s
The 389 is the block under most early GTOs and full-size Pontiacs, and it is usually torn down for one of two reasons: it needs to go back together right, or it needs to be more engine than it was. A rotating assembly answers both, because stroke, bore, piston shape and compression are all decided in the same package.
Butler splits 389 block work into three paths — stock-stroke rebuilder assemblies and rebuild kits, stroker assemblies up to 4.250", and super stroker assemblies up to 4.500" — all built around Ross forged pistons and balanced in our own shop.
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More About 389 Blocks (395-480 cu. In.)
1. Which of the three subcategories you belong in
The 389 pages are split by stroke, because stroke is what separates a rebuild from a build.
| 389 Engine Rebuilder Assemblies — Stock Stroke | Re-ring kits, complete rebuild kits with cast or forged pistons, and the Butler/Ross custom balanced assembly on the stock 3.750" stroke with I-beam 6.625" rods. The right shelf when the car stays a 389 and you want it fresh. |
| 389 Stroker Rotating Assemblies — up to 4.250" stroke | Butler's balanced long-rod stroker assemblies at 4.000" stroke for 421-427 ci and 4.250" stroke for 447-454 ci. |
| 389 Super Stroker Rotating Assemblies — up to 4.500" stroke | The 4.500" stroke assembly, 473-480 ci, which is as far as a 389 block goes here. |
2. What a 389 block gets you
The 389 has a useful head start on a 400 build: the block is already there, and the same Butler assemblies that take it to the top of this range use the same Ross forgings and the same rod lengths as the rest of the Pontiac line.
| Rod length steps with stroke | 6.625" rods on the stock-stroke assembly, 6.700" at 4.000" stroke, 6.800" at 4.250" stroke. Butler's long-rod approach is the reason each stroke gets its own rod, not a spacer and a hope. |
| Pistons | Butler/Ross forged flat top, dish or dome on the exclusive true-Pontiac forging, machined to a compression ratio you specify once you tell us the chamber cc of your heads. |
| Everything balanced | Assemblies are internally balanced through the Butler Process — rods and pistons weighed and pin-fitted, crank computer balanced to the assembly, balance card in the box. |
3. Two things to settle before you order
| Check the casting number | Blocks whose casting numbers end in 557 have thinner main webbing. Butler suggests limiting those to 4.000" stroke and under 500 hp. |
| Neutral balance parts | An internally balanced assembly needs a neutral-balanced flexplate or flywheel and a neutral harmonic balancer. Budget for those at the same time as the assembly, not after it is in the car. |
If the 389 is numbers-matching and staying that way, start in the rebuilder assemblies. If it is a driver and you want the cubic inches, the stroker and super stroker pages are where the real gains live.
389 Stroker Rotating Assemblies- Up to 4.250 Stroke
Not sure what your Pontiac needs?
Email our tech team at tech@butlerperformance.com. Tell us your engine, heads, car, and power goal, and we will put the parts together as one combination that works.