- Home »
- Catalog »
- Rotating Assemblies & Stroker Kits »
- 389 Blocks (395-480 cu. In.) »
- 389 Stroker Rotating Assemblies- Up to 4.250 Stroke
389 Stroker Rotating Assemblies- Up to 4.250 Stroke
Pontiac V8 389 Stroker Rotating Assemblies- Up to 4.250 Stroke
Cubic Inches from the Block You Have — 389 Stroker Rotating Assemblies- Up to 4.250 Stroke for Pontiac V8s
A 389 stroker is the cheapest cubic inch a 389 owner can buy, because the block is already in the car. Swapping to a longer-stroke crank with matching rods and pistons turns a 389 into something that pulls like a big-inch Pontiac without changing anything outside the engine.
Butler builds two stroker rotating assemblies for the 389 block in this range — a 4.000" stroke at 421-427 ci and a 4.250" stroke at 447-454 ci — both long-rod, both on Butler/Ross forged pistons, both internally balanced here before they ship.
Browse 389 Stroker Rotating Assemblies- Up to 4.250 Stroke Products
Popular Brands:
More About 389 Stroker Rotating Assemblies- Up to 4.250 Stroke
1. The two assemblies
Both are balanced, long-rod packages. The difference is the crank and the rod that goes with it.
| 4.000" stroke, 421-427 ci | New forged 4.000" crank, forged flat top Ross pistons with dish or dome available, bushed and full-float H-beam 6.700" rods, 990 wrist pins, Total Seal Classic Race rings and Federal Mogul or Clevite Performance bearings. Nitrous-safe. |
| 4.250" stroke, 447-454 ci | New cast or forged 4.250" crank, forged flat top Ross pistons with dish or dome available, bushed and full-float H-beam 6.800" rods, 990 pins, Total Seal Classic Race rings and rod bearings selected for proper clearance in our shop. |
2. Why long rods
Butler steps the rod length up with the stroke instead of using one rod for everything. The 6.700" and 6.800" rods keep the pin height and rod angle sensible at the longer strokes, which is the whole point of the long-rod approach — durability and performance rather than just a bigger number on the crank box.
| Pistons | Genuine Ross forgings on Butler's exclusive true-Pontiac strut-style design, not the cheaper pistons sold at similar money. Flat top, or a custom dish machined to the compression ratio you ask for. |
| Compression | Tell us the chamber cc of your heads and the compression you want; our techs work with Ross to design the piston to hit it. Custom dish pistons carry a 10 to 12 week lead time. |
| Rings | Total Seal Classic Race plasma-moly as standard, with AP Advanced Stainless for longer life and tighter tolerance, or Gapless Top to seal cylinder pressure between the top and second ring. |
3. Before you commit the block
| Casting check | Blocks with casting numbers ending in 557 have thinner main webbing. Butler suggests limiting those to 4.000" stroke and under 500 hp, which points straight at the 421-427 assembly rather than the 447-454. |
| Bore and honing | Bore options start at .030" over so the block cleans up and the rings seat in spec. Have the pistons in hand when the block is honed. |
| Balance hardware | These are internally balanced by Butler, so the flexplate or flywheel and the harmonic balancer both need to be neutral. |
If you want to go past this range, the 4.500" super stroker assembly for the 389 block is on its own page. Anything in between, call and we will talk through what the block and the heads will support.
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.