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455 Block
Pontiac V8 455 Block
Largest Factory Bore — 455 Block for Pontiac V8s
455 Block rings cover the largest factory Pontiac bore, from a 4.150" standard through 4.216" on a well-opened block. The 455 also uses a different stock ring pack than a 400 or 428, so a set that looks close on paper can be wrong on the second ring.
Butler stocks Sealed Power moly-faced replacement sets in standard through .060" over, plus Total Seal Classic Race drop-in and file fit sets and gapless top ring sets for performance and stroker 455 builds.
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1. The 455 stock ring pack is not the 400 pack
This is the detail that catches people. The Sealed Power replacement sets for a 455 use a 5/64" top, a 1/16" second and a 3/16" oil ring. The equivalent 400 and 428 sets use a 5/64" second. Same brand, same family, different middle ring.
| Standard bore, 4.150" | The factory 455 bore, for a block that honed clean. |
| .030" over, 4.180" | The common rebuild size. |
| .040" over, 4.190" | The next step when a cylinder needs more cleanup. |
| .060" over, 4.210" | About as far as most factory 455 castings should be taken, and only after a sonic check. |
2. Total Seal Classic Race for performance 455 builds
| Drop in | Pre-gapped Classic Race sets at 4.181" and 4.191" in a 1/16, 1/16, 3/16 pack. |
| File fit | Supplied oversize so you set the gap. Covers 4.180" to 4.181" as a 4.186" ring, 4.185" as a 4.190" ring, 4.190" to 4.191" as a 4.195" ring, and 4.216". |
| Which one | Drop in suits a mild street 455. File fit is the answer whenever there is boost, nitrous or sustained rpm in the plan, because the end gap becomes your decision rather than the factory's. |
3. Gapless top rings and the big bore end of the range
| Gapless top, 4.180" to 4.181" | Total Seal file fit set supplied as a 4.185" ring. The gapless top design closes the route blow-by normally takes past the top ring. |
| Gapless top, 4.211" | File fit set supplied as a 4.216" ring, for a 455 taken to the upper end of its bore range. |
| Above .060" over | Bores in the 4.211" and 4.216" range are stroker territory and belong on a block that has been sonic tested. The rings exist; make sure the cylinder wall does too. |
4. Ordering without a mistake
| Order to the honed bore | Not to the nominal overbore, and not to what the machinist intended. Butler's own note on these sets is to match the ring set to the finished bore and to call if you are unsure. |
| Thickness follows the piston | A stock replacement 455 piston is grooved for the 5/64, 1/16, 3/16 pack. A forged performance piston is usually 1/16, 1/16, 3/16. The piston decides, not the block. |
| Not listed | If the bore or ring thickness you need is not shown, Butler will either have it in stock or can get it. |
5. Filing the gap on a 455
File fit rings arrive a few thousandths oversize so the end gap is yours to set. Square each ring in the cylinder it will live in, measure with a feeler gauge, file the end square, deburr it and keep that ring with that bore. A mild pump gas 455 wants a tighter gap than one running nitrous or boost, and that is the whole point of buying a file fit set instead of a drop in.
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.