Description
About This Engine
The Pontiac 455 is the largest displacement production V8 Pontiac ever built. Introduced for the 1970 model year by expanding the bore of the 428 to 4.155 inches and extending the stroke to 4.21 inches, it displaced an actual 457.6 cubic inches and delivered one of the most torque-heavy power curves of the entire muscle car era. At its peak, the 455 HO produced 370 hp and 500 lb-ft of torque – figures that put it among the most powerful street engines available anywhere at the time.
One characteristic that sets the Pontiac 455 apart: all Pontiac V8 engines from the 326 through the 455 share identical external block dimensions and motor mount locations. This means the 455 physically bolts into any vehicle originally using any Pontiac V8, making swaps and replacements straightforward with the correct supporting components.
The 455 powered the GTO, Firebird, Trans Am, Grand Prix, LeMans, Catalina, Bonneville, and Grand Ville through 1976. Today, a documented used OEM unit with known casting numbers and a confirmed variant is the foundation every serious Pontiac restoration builds on.
Signs You Need a Replacement Engine
- Knock or rattle under load – rod or main bearing wear on high-mileage units
- Blue smoke on startup or under acceleration – worn valve seals or piston rings
- Loss of compression on one or more cylinders – scored walls, worn rings, or head gasket failure
- Low oil pressure at idle on a warmed-up engine – main bearing clearance out of tolerance
- Coolant in the oil or white exhaust smoke – head gasket failure, common on late-emission blocks run hot
- Rough idle that worsens as the engine warms – worn cam lobes, a known high-mileage Pontiac V8 issue
- Excessive oil consumption beyond 1 quart per 1,500 miles – valve stem seal or ring failure
Known Problems With This Engine
- Late-emissions output drop: The 1975 and 1976 455s produced as little as 200 hp at 7.6:1 compression. Fine for a stock replacement, not suitable as a performance build core. We document the year and variant before shipping.
- 2-bolt main caps from 1973 onward on base blocks: After 1972, standard 455 blocks switched from 4-bolt to 2-bolt main caps. Super Duty units retained 4-bolt. If your build requires 4-bolt, specify during the quote process.
- Round-port vs D-port head intake incompatibility: 1970 base 455s used D-port cylinder heads. 1971 onward HO engines used round-port heads requiring a different intake manifold. We document the head casting before every order ships.
- Oil pump drive wear: High-mileage Pontiac V8s can develop wear in the oil pump driveshaft area. We inspect and record oil pressure on every unit.
- Rear main seal seepage: Two-piece rear main seals on these engines seep on aged units. We inspect all gasket surfaces and disclose any seepage before shipping.
Known Variants by Year and Output
| Variant | Years | HP | Torque | Compression | Notes |
|---|---|---|---|---|---|
| Base 455 | 1970 | 360-370 hp | 500 lb-ft | 10.25:1 | D-port heads. 370 hp Grand Prix/GTO. 360 hp full-size. |
| 455 HO | 1971 | 335 hp (gross) | 480 lb-ft | 8.4:1 | Round-port heads. Best street performer of the run. |
| 455 HO | 1972 | 300 hp (net) | 415 lb-ft | 8.2:1 | Same engine. New SAE net rating system. |
| 455 SD (Super Duty) | 1973-1974 | 290 hp (net) | 390 lb-ft | 8.4:1 | Most powerful 455 built. 4-bolt mains. Rarest. |
| Base 455 | 1973 | 250 hp (net) | 370 lb-ft | 8.0:1 | 2-bolt mains from this year on base engines. |
| Base 455 | 1975-1976 | 200 hp (net) | 330 lb-ft | 7.6:1 | Lowest output. Stock replacement only. |
Common Casting Numbers
| Casting Number | Application |
|---|---|
| 9799140 | 1970 – all Pontiac applications |
| 485428 / 485429 | Common 1971-1974 blocks |
| 500813 | 1975-1976 late emissions-era blocks |
What Is Included / What Is Not Included
INCLUDED (Long Block): Block, crankshaft, pistons, connecting rods, camshaft, cylinder heads, valve train, oil pan, timing cover, and water pump where present.
NOT INCLUDED: Intake manifold, carburetor, exhaust manifolds, distributor, ignition system, alternator, power steering pump, A/C compressor, starter, flexplate or flywheel, accessory brackets.
No Core Charge: You are not required to return your old engine.
Vehicle Compatibility – Direct Fit
| Vehicle | Years |
|---|---|
| Pontiac GTO | 1970 to 1973 |
| Pontiac Firebird | 1971 to 1976 |
| Pontiac Trans Am | 1971 to 1976 |
| Pontiac Grand Prix | 1970 to 1976 |
| Pontiac LeMans | 1970 to 1976 |
| Pontiac Catalina | 1970 to 1976 |
| Pontiac Bonneville | 1970 to 1976 |
| Pontiac Grand Ville | 1972 to 1976 |
Swap compatibility: The 455 bolts into any 1967-and-newer Pontiac originally equipped with any Pontiac V8. Transmission compatibility: TH400 (strongest) | TH350 | Muncie 4-speed M20/M21/M22.
Common Names and Search Terms
Pontiac 455 | 455 Pontiac engine | Pontiac 455 motor | 455 HO engine for sale | 455 Super Duty for sale | Pontiac GTO engine for sale | Pontiac Trans Am 455 engine | Pontiac Firebird 455 | 455 Pontiac big block | Pontiac 7.5L engine
Used OEM vs Rebuilt – Which Is Right for You
Used OEM is the right choice for a GTO, Trans Am, or Firebird restoration – particularly where period-correct condition matters. Our 455s are compression tested with casting numbers and variant documented. A professionally rebuilt unit makes sense for a show car or specific tolerance build. Rebuilt HO and SD units typically run $5,000 to $9,000 or more from specialists. Call us to discuss sourcing options.
Condition and Inspection Process
- Compression test across all 8 cylinders – pressure per cylinder recorded
- Visual inspection of block for cracks, deck damage, scored journals, stripped threads
- Leak check on all gasket surfaces for active oil or coolant seepage
- Valve cover inspection for sludge and cam wear indicators
- Casting number, date code, and variant confirmed – D-port or round-port head noted
- Main cap configuration confirmed – 2-bolt or 4-bolt noted before shipping
Buyer Tips – What to Know Before You Order
- Know your variant: HO (round-port heads 1971-1973), Super Duty (1973-1974, rarest), and base units have different characteristics. Specify when calling.
- Round-port vs D-port intake: If your vehicle has an HO engine, the intake manifold is round-port specific. A D-port intake will not fit on an HO block without a head change.
- 4-bolt vs 2-bolt mains: All pre-1973 standard 455s and all Super Duty units have 4-bolt mains. Post-1972 base engines use 2-bolt. Specify if 4-bolt is required.
- Crankshaft interchangeability: Pontiac 455 cranks are interchangeable with the 400, enabling stroker builds.
Why Buy From Vaz Auto Solutions
- Variant confirmed before you pay – HO, SD, or base documented including head type and main cap configuration
- Casting number and date code on record for every unit
- Compression tested across all 8 cylinders – results shared before order is confirmed
- Fitment verified for your specific Pontiac vehicle before every order ships
- No core charge – keep your old engine
- Free freight pallet delivery to all 50 states, no hidden fees
- 15 day replacement warranty on internal engine defects
- Call (240) 301-0095 – someone who understands 455 variants, casting differences, and Pontiac restoration
Rick M. –
Found a 1971-era 455 for my GTO project. Vaz confirmed the D-port vs round-port question upfront and matched me to the right unit. Light seepage at the rear main gasket – disclosed before shipping and cleaned up with a new seal during the build. Good engine, honest company.
David K. –
Bought a 455 HO for my 1972 Trans Am restoration. Vaz confirmed the round-port heads and documented the casting number before I paid. Compression came back 155 to 162 across all 8 – solid numbers for a used engine. Dropped in and fired on the third crank. Exactly what a Trans Am should sound like.